Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013.

P-40 Introduction
P-41 Seniority order for classes
P-42 Seniority order for acids
P-43 Seniority order for suffixes
P-44 Seniority order for parent structures
P-45 Selection of the preferred IUPAC name
P-46 The principal chain in substituent groups

P-40 INTRODUCTION

In this Chapter, principles regarding name construction are presented. It is recognized that in chemical discussions it may sometimes be convenient to depart from rigorous rules in order to provide a name more appropriate to the chemical intent or to avoid obscuring an important feature. However, such deviations should not be done without good reason, and names so derived are not recommended for general use in publications.

The application of the principles and rules described in this Chapter has been devised to lead to a preferred IUPAC name. Preferred IUPAC names are not necessarily the aim of a practicing chemist who wants to communicate with his colleagues in familiar, well understood terms, but it may be appropriate to those who cite chemical names in legislative documents, in international trade and commerce, or for preparing programs for index purposes, databases, and retrieval systems.

This Chapter includes the general rules and orders of seniority used in substitutive nomenclature and in other types of nomenclature when required.

P-41 SENIORITY ORDER FOR CLASSES

The order of seniority of classes is given in Table 4.1. It ranks classes expressed by suffixes (classes 1 through 20) and classes based on the senior atom in compounds (classes 21 through 43).

1 Radicals

2 Radical anions

3 Radical cations

4 Anions

5 Zwitterions

6 Cations

7 Acids

7a ‘Suffix’ acids in the order carboxylic (not including carbonic or polycarbonic acids, which belong to sub-class ‘7b’), sulfonic, sulfinic, selenonic, seleninic, telluronic, tellurinic, each followed in turn by the corresponding peroxy, imidic, and hydrazonic acids. Chalcogen analogues follow each of the corresponding oxygen acids and, in each case, the chalcogen analogue with the greater number of the preferred chalcogen atom (O > S > Se > Te), considered first in −OOH groups, then in −OH groups as necessary. (See P-42 for the complete list of seniority of acids, P-43 for suffixes modified by functional replacement, and Table 4.4 for an extensive list of the order of seniority of all these suffixes.)

7b Carbon acids with no substitutable hydrogen atoms in the order polynuclear carbonic acids (tricarbonic acid, dicarbonic acid), then carbonic acid, and cyanic acid.

7c Oxoacids having substitutable hydrogen atoms attached to their central atoms and their acidic derivatives in the following decreasing order of seniority: azonic, azinic, phosphonic, phosphinic, phosphonous, phosphinous acids, etc. (see P-42 for the complete list).

7d Mononuclear and polynuclear oxoacids other than carbon acids without substitutable hydrogen atoms attached to their central atom (see 7b, above), but which may be functionalized or may form derivatives by functional replacement, which have substitutable hydrogen atoms.

7e Other monobasic ‘oxoacids’ used as functional parent compounds.

8 Anhydrides [substitutive nomenclature is used for cyclic anhydrides that are named as heterocycles (see 16 below); functional class names are given to acyclic anhydrides and to a few cyclic anhydrides corresponding to acids having retained names; cyclic anhydrides are preferred over noncyclic anhydrides, when functional names are used].

9 Esters (functional class names are given to noncyclic esters; lactones and other cyclic esters are named as heterocycles; see 16 below).

10 Acid halides and pseudohalides [first in the order of the corresponding acid given above, then in the order of the halogen atoms (–F > –Cl > –Br > –I); then in the following order of pseudohalogen groups ( –N₃ > –CN > –NC > –NCO > –NCS > –NCSe > –NCTe > –CNO).

11 Amides [in the order of the corresponding acids; cyclic amides are named as heterocycles (see class 16 below)].

12 Hydrazides (in the order of the corresponding acids).

13 Imides (includes only cyclic imides derived from organic di- or polybasic acids having retained names).

14 Nitriles.

15 Aldehydes and chalcogen analogues.

16 Ketones (of the type –C-CO-C–), pseudoketones (of the type –C-CO-X , X-CO-X, or –CO-X-CO–, where X ≠ C, halogen, pseudohalogen, or NH₂, see P-64.1.2) and heterones (see P-64.4). See Classes 8, 9, 11 and 13, on lactones, lactams, anhydrides, imides.

17 Hydroxy compounds and chalcogen analogues (includes alcohols and phenols, which no longer have a separate ranking order).

18 Hydroperoxides (peroxols), i.e., –OOH.

19 Amines (defined as having three single covalent attachments to a nitrogen atom, i.e., NR₃).

20 Imines, R=NH or R=N-R′.

Classes denoted by the senior atom in heterane nomenclature

21 Nitrogen compounds: heterocycles, polyazanes, hydrazines (except for hydrazides), diazenes, hydroxylamines, azanes (except for amides, amines, and imines)

22 Phosphorus compounds: heterocycles, polyphosphanes, phosphanes

23 Arsenic compounds: heterocycles, polyarsanes, arsanes

24 Antimony compounds: heterocycles, polystibanes, stibanes

25 Bismuth compounds: heterocycles, polybismuthanes, bismuthanes

26 Silicon compounds: heterocycles, polysilanes, silanes

27 Germanium compounds: heterocycles, polygermanes, germanes

28 Tin compounds: heterocycles, polystannanes, stannanes

29 Lead compounds: heterocycles, polyplumbanes, plumbanes

30 Boron compounds: heterocycles, polyboranes, boranes

31 Aluminium compounds: heterocycles, polyalumanes, alumanes

32 Gallium compounds: heterocycles, polygallanes, gallanes

33 Indium compounds: heterocycles, polyindiganes, indiganes

34 Thallium compounds: heterocycles, polythallanes, thallanes

35 Oxygen compounds: heterocycles, polyoxidanes (trioxidane but not peroxides or ethers)

36 Sulfur compounds: heterocycles, polysulfanes (trisulfane, λ⁶ and λ⁴ mono and disulfanes, but not disulfides or sulfides)

37 Selenium compounds: heterocycles, polyselanes (triselane but not diselenides, selenides)

38 Tellurium compounds: heterocycles, polytellanes (tritellane but not ditellurides, tellurides)

39 λ⁷, λ⁵ and λ³ halogen compounds in the order F > Cl > Br > I.

40 Carbon compounds: rings, chains

41 Ethers, then sulfides, sulfoxides, sulfones; then selenides, selenoxides, etc.

42 Peroxides, then chalcogen analogues with the greater number of the senior chalcogen atom, where O > S > Se > Te.

43 λ¹ Halogen compounds in the order F > Cl > Br > I

Examples:

Acids of class 7 (see Table 4.1) in the order of classes of compounds are further classified into subclasses. These correspond to acids expressed by suffixes and acids used as functional parents (see P-34). The following subsections complete the brief description given in Class 7; the acids are described in decreasing seniority order.

P-42.1 Class 7a. Acids expressed by suffixes (excludes carbonic and polycarbonic acids)
P-42.2 Class 7b. Carbon acids with no substitutable hydrogen atoms
P-42.3 Class 7c. Noncarbon acids having substitutable hydrogen atoms on the central atom
P-42.4 Class 7d. Noncarbon acids used to generate derivatives having substitutable hydrogen atoms
P-42.5 Class 7e. Other monobasic ‘oxo’ acids used as functional parents.

P-42.2 CLASS 7b. CARBON ACIDS WITH NO SUBSTITUTABLE HYDROGEN ATOMS

All these names are preselected names. In this class, criteria for seniority are, in descending order:

(a) the central atom first in the list N > P > As > Sb > B;

(b) maximum number of central atoms;

(c) homopolyacids (isopolyacids) (see ref. 12);

(d) having contiguous central atoms;

(e) maximum number of acidic (–OH) groups;

(f) highest oxidation number for the central atom

For consistency in the names of polynuclear oxoacids, the numerical infix ‘di’ has been uniformly used in naming dinuclear ‘hypo’ acids, for example hypodiphosphorous acid, rather than hypophosphorous acid.

P-42.4 CLASS 7d. NONCARBON ACIDS USED TO GENERATE DERIVATIVES HAVING SUBSTITUTABLE HYDROGEN ATOMS

All these names are preselected names.

In this class, criteria for seniority are, in descending order:

(a) the central atom first in the list: P > As > Sb > Si > B > S > Se >Te;

(b) maximum number of central atoms;

(c) homopolyacids (isopolyacids) (see ref. 12);

(d) polyacids having contiguous central atoms;

(e) maximum number of acidic groups (-OH groups);

(f) highest oxidation number for the central atom.

polyphosphoric acids	(HO)2P(O)-O-[PO(OH)-O-]nP(O)(OH)2
polyphosphorous acids	(HO)2P-O-[P(OH)-O-]n-P(OH)2
tetraphosphoric acid	(HO)2P(O)-O-P(O)(OH)-O-P(O)(OH)-O-P(O)(OH)2
triphosphoric acid	(HO)2P(O)-O-P(O)(OH)-O-P(O)(OH)2
diphosphoric acid	(HO)2P(O)-O-P(O)(OH)2
diphosphorous acid	(HO)2P-O-P(OH)2
hypodiphosphoric acid (for the prefix ‘hypodi’ see P-67.2.1)	(HO)2(O)P-P(O)(OH)2
hypodiphosphorous acid (for the prefix ‘hypodi’ see P-67.2.1)	(HO)2P-P(OH)2
phosphoric acid	P(O)(OH)3
phosphorous acid	P(OH)3
polyarsoric acids > polyarsorous acids > diarsoric acid > diarsorous acid > hypodiarsoric acid > hypodiarsorous acid (for the prefix ‘hypodi’ see P-67.2.1)
arsoric acid	As(O)(OH)3
arsorous acid	As(OH)3
polystiboric acids > polystiborous acid > distiboric acid > distiborous acid > hypodistiboric acid > hypodistiborous acid (for the prefix ‘hypodi’ see P-67.2.1)
stiboric acid	Sb(O)(OH)3
stiborous acid	Sb(OH)3
silicic acid	Si(OH)4
(formerly orthosilicic acid. See P-67.1.1.1, P-67.1.2.2 and Table IR-8.1, ref. 12.)
diboric acid	(HO)2B-O-B(OH)2
hypodiboric acid (for the prefix ‘hypodi’ see P-67.2.1)	(HO)2B-B(OH)2
boric acid	B(OH)3
polysulfuric acids	(HO)SO2-O-[SO2-O-]nSO2(OH)
polysulfurous acids	(HO)SO-O-[SO-O-]nSO(OH)
disulfuric acid	(HO)SO2-O-SO2(OH)
disulfurous acid (ambiguous see P-67.3.2)	(HO)S(O)-O-S(O)(OH)
dithionic acid (hypodisulfuric acid) (for the prefix ‘hypodi’ see P-67.2.1)	(HO)O2S-SO2(OH)
dithionous acid (hypodisulfurous acid)	(HO)(O)S-S(O)(OH)
sulfuric acid	S(O)2(OH)2
sulfurous acid	S(O)(OH)2
polyselenic acids > polyselenous acids > diselenic acid > diselenous acid > hypodiselenic acid > hypodiselenous acid (for the prefix ‘hypodi’ see P-67.2.1)
selenic acid	Se(O)2(OH)2
selenous acid	Se(O)(OH)2
polytelluric acids > polytellurous acids > ditelluric acid > ditellurous acid > hypoditelluric acid > hypoditellurous acid (for the prefix ‘hypodi’ see P-67.2.1)
telluric acid	Te(O)2(OH)2
tellurous acid	Te(O)(OH)2

P-42.5 CLASS 7e. OTHER MONOBASIC ‘OXO’ ACIDS USED AS FUNCTIONAL PARENTS

All these names are preselected names. In this class, criteria for seniority are, in descending order:

(a) the central atom first in the list N > F > Cl > Br > I;

(b) highest oxidation number for the central atom.

P-43 SENIORITY ORDER FOR SUFFIXES

P-43.0 Introduction
P-43.1 General methodology of functional replacement

Suffixes are modified as indicated in Table 4.3 for acids and in Table 4.4 for all substituent suffixes. The order of seniority for suffixes is described in this Section. It is based on the seniority of classes 7 through 20 given in Table 4.1 and includes suffixes modified by functional replacement.

P-43.1 GENERAL METHODOLOGY OF FUNCTIONAL REPLACEMENT

Suffixes are modified as indicated in Table 4.3 for acids and in Table 4.4 for acids and other classes. Prefixes and infixes are used as indicated in Table 4.2. Prefixes are used to modify suffixes such as ‘ol’, ‘al’, for example ‘thiol’ and ‘thial’. Infixes are recommended to modify the suffixes ‘carboxylic acid’, ‘sulfonic acid’, and related suffixes, for example ‘carboperoxoic acid’ and ‘sulfonothioic acid’.

When several oxygen atoms are replaceable, the following criteria are applied, in order, until a decision is reached:

(a) maximum number of oxygen atoms, then S, Se, and Te atoms, =NH and =NNH₂ groups;

(b) maximum number of oxygen atoms, then S, Se, and Te atoms, in −OO− groups;

(c) oxygen atoms, then S, Se, and Te atoms, in −(O)OH and −OH groups.

Table 4.3 gives the list, in decreasing order, of the seniority of suffixes and suffixes modified by functional replacement for carboxylic and sulfonic acids. Sulfinic acid suffixes are similar to sulfonic acids. Selenium and tellurium acid suffixes are formed by replacing ‘sulf’ by ‘selen’ or ‘tellur’.

P-44 SENIORITY ORDER FOR PARENT STRUCTURES

A parent structure is defined (P-15.1.1 and P-15.1.2) as a parent hydride, for example methane, a functionalized parent hydride, for example, cyclohexanol, or a functional parent compound, for example, acetic acid. For choice of the preferred IUPAC name based on a senior parent structure, see P-45.

P-44.0 Introduction
P-44.1 Seniority order for parent structures
P-44.2 Seniority order only for rings and ring systems
P-44.3 Seniority of acyclic chains (the principal chain)
P-44.4 Seniority criteria applicable to rings, ring systems, or acyclic chains

The selection of a preferred parent structure is based on the seniority of classes (see P-41), which gives priority first to characteristic groups expressed as suffixes and then to parent hydrides when different classes are present. Section P-44.1 covers the selection of a preferred parent structure when different classes are involved and the selection between rings and chains in the same class. When there is a choice among cyclic parent hydrides, the senior ring or ring system is chosen in accord with the seniority order of rings and ring systems (see P-44.2). When there is a choice among acyclic parent hydrides a principal chain must be chosen (see P-44.3). The three seniority orders, for classes, rings and ring systems, and the principal chain, are expressed in a general seniority order called ‘seniority order for parent structures’. Section P-44.4 covers criteria for selection of a senior parent structure applicable to either rings, ring systems, or acyclic chains.

A thorough revision and extension of the seniority order of classes, of rings and ring systems, and for selecting the principal chain was needed in the context of preferred names. This revision incorporates a major change from earlier recommendations given in the 1979 edition (ref. 1) and the 1993 Guide (ref. 2).

In acyclic parent structures the order of seniority between unsaturation and length of chain given in earlier recommendations is reversed. Thus, the first criterion to be considered in choosing a preferred parent acyclic chain is the length of the chain; unsaturation is now the second criterion.

Note 1: Since the senior parent structure can occur in a compound in multiple ways, several plausible, unambiguous names can be generated. The criteria necessary to select a preferred IUPAC name are described in P-45; thus, traditional criteria related to substituent groups are not incorporated in this Section.

Note 2: Criteria related to nonstandard bonding have been incorporated into the criteria applicable to either rings, ring systems, or acyclic chains (P-44.4); hierarchically, they come after the criteria related to unsaturation (double bonds) and before those related to indicated hydrogen atoms.

P-44.1 SENIORITY ORDER FOR PARENT STRUCTURES

When there is a choice, the senior parent structure is chosen by applying the following criteria, in order, until a decision is reached. These criteria must always be applied before those applicable to rings and ring systems (see P-44.2) and to chains (see P-44.3). Then criteria applicable to both chains and rings or ring systems given in P-44.4 are considered.

P-44.1.1 The senior parent structure has the maximum number of substituents corresponding to the principal characteristic group (suffix) or senior parent hydride in accord with the seniority of classes (P-41) and the seniority of suffixes (P-43).

Examples:

3-cyclohexylpropanoic acid (PIN)
cyclohexanepropanoic acid (see P-15.6)

3-propylbenzoic acid (PIN)

3-(4-chlorobutyl)pentane-1,4-diol (PIN)
[not 7-chloro-3-(1-hydroxyethyl)heptan-1-ol;
there are two of the principal characteristic groups
in the parent of the PIN and only one in the other name]
[not 3-(4-chlorobutyl)pentane-2,5-diol;
the locant set ‘1,4’ for the principal characteristic groups
of the PIN is lower than ‘2,5’]

NH₂-NH-COOH
hydrazinecarboxylic acid (PIN)

H₃Si-CH₂-CH₂-COOH
3-silylpropanoic acid (PIN)

HOOC-SiH₂-CH₂-CH₃
ethylsilanecarboxylic acid (PIN)

7,7-bis[(2-butoxyethoxy)methyl]-3,6,10,13-tetrathiapentadecane-1,15-dioic acid (PIN)
[not 9-[(2-butoxyethoxy)methyl]-9-({2-[(carboxymethyl)sulfanyl]ethyl}sulfanyl)-11,14-dioxa-3,6-dithiaoctadecan-1-oic acid;
nor 7-[(2-butoxyethoxy)methyl]-7-[2-({2-[(carboxymethyl)sulfanyl]ethyl}sulfanyl)ethyl]-9,12-dioxa-3,6-dithiahexadecan-1-oic acid;
there are two of the principal characteristic group in the parent of the PIN and only one in the other names]

H₃Si-CH₂-CH₂-SiH₂-CH₂-CH₂-SiH₃
[silanediyldi(ethane-2,1-diyl)]bis(silane) (PIN)
(Si is senior to C, see P-44.1.2)
[not bis(2-silylethyl)silane;
the multiplicative preferred name expresses two occurrences of the parent hydride silane;
the substitutive name expresses only one]

4-{4-[(pyridin-4-yl)methyl]phenyl}-1,7(1),3(1,3),5(1,4)-tetrabenzenaheptaphane-1⁴,7⁴-dicarboxylic acid (PIN)
[not 4-{[4-(4-carboxyphenyl)methyl]phenyl}-1(4)-pyridina-3(1,4),5(1,3),7(1)-tribenzenaheptaphane-7⁴-carboxylic acid;
nor 4-{[3-(4-carboxyphenyl)methyl]phenyl}-1(4)-pyridina-3,5(1,4),7(1)-tribenzenaheptaphane-7⁴-carboxylic acid;
there are two of the principal characteristic group in the PIN and only one in the other names]

P-44.1.2.1 When two or more atoms denoting different classes are present in a compound, and when the choice for parent compound is between these atoms, the parent compound is the one belonging to the class cited first in the seniority of classes given above. A single senior atom is sufficient to give seniority to the parent hydride.

This rule is broader than Rule D-1.34 in the 1979 Recommendations (ref. 1) that referred to compounds where the heteroatoms were directly attached to each other.

Examples:

Two methods are recognized to name systems composed of rings and chains (exclusive of linear phanes).

(1) Within the same class, a ring or ring system has seniority over a chain. When a ring and a chain contain the same senior element, the ring is chosen as parent. Rings and chains are chosen regardless of their degree of hydrogenation. As a consequence, this approach prefers the choice of a ring over a chain in systems composed of cyclic and acyclic hydrocarbons.

(2) The context may favor the ring or the chain, so that, for example, substituents may be treated alike or an unsaturated acyclic structure may be recognized, or the one chosen has the greater number of skeletal atoms in the ring or in the principal chain of the acyclic structure.

In the examples that follow, when a choice is possible, names formed by both methods are given. For selection of a preferred IUPAC name, see P-52.2.8.

Examples:

(1) heptylbenzene (PIN)
(ring is senior to chain)
(2) 1-phenylheptane
(chain has greater number of skeletal atoms)

(1) ethenylcyclohexane (PIN)
(ring is senior to chain)
(2) cyclohexylethene
(emphasizes unsaturation)

(1) 1,1′-methylenedibenzene (PIN)
(ring is senior to chain)
(2) diphenylmethane
(treats phenyl groups alike as substituents)

(1) 1,1′-(ethene-1,2-diyl)dicyclohexane (PIN)
(ring is senior to chain)
(2) 1,2-dicyclohexylethene
(emphasizes unsaturation)

(1) 2-hydrazinylpyridine (PIN)
(ring is senior to chain)
(2) (pyridin-2-yl)hydrazine
(pyridin-2-yl)diazane

(1) 2-hydrazinyl-4,5-dihydro-1H-imidazole (PIN)
2-diazanyl-4,5-dihydro-1H-imidazole
(ring is senior to chain)
(2) (4,5-dihydro-1H-imidazol-2-yl)hydrazine

P-44.1.4 Seniority among acyclic chains (the principal chain). Criteria that apply only when the choice for parent structure is between two or more acyclic chains are given in P-44.3.

P-44.1.5 Criteria applicable to rings, ring systems, or acyclic chains, such as unsaturation, the presence of skeletal atoms with different bonding numbers, isotopically modified compounds, and stereochemical configurations are given in P-44.4.

P-44.2 SENIORITY ORDER ONLY FOR RINGS AND RING SYSTEMS

P-44.2.1 Criteria general to all rings and ring systems (other than phanes, both cyclic and linear, for which see P-44.2.2.2.2 and P-44.2.2.2.6, respectively)
P-44.2.2 Criteria specific to a particular kind of ring or ring system

The senior ring or ring system:

(a) is a heterocycle;

(b) has at least one nitrogen atom;

(c) has at least one heteroatom (in the absence of nitrogen) that occurs earlier in the following sequence: F > Cl > Br > I > O > S > Se > Te > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl;

(d) has the greater number of rings;

(e) has the greater number of skeletal atoms;

(f) has the greater number of heteroatoms of any kind;

(g) has the greater number of heteroatoms occurring earlier in the sequence: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl.

In order to apply P-44.2 after P-44.1 has failed to reach a conclusion, there must not be a characteristic group present in the compound, or the same number of a characteristic group must be present in all cyclic structures to be compared. In the following examples, as well as examples throughout P-44.2, seniority is expressed by the symbol ‘>’ to be read as ‘senior to’. In the case of larger structures the phrase ‘is senior to’ is cited between the senior structure and the less senior structure.

Examples (the symbol > means ‘is senior to’):

2-[(naphthalen-2-yl)methyl]pyridine (PIN)
(pyridine > naphthalene)

1,8-di(bicyclo[3.2.1]octan-3-yl)anthracene (PIN)

4-[(4-fluoro-2-methyl-1H-indol-5-yl)oxy]-6-methoxy-7-[3-(pyrrolidin- 1-yl)propoxy]quinazoline (PIN)
(quinazoline > indole > pyrrolidine)

4-(6-{2-[(3-methylphenyl)methylidene]hydrazin-1-yl}-2-[2-(pyridin-2-yl)ethoxy]pyrimidin-4-yl)morpholine (PIN)
(morpholine > pyrimidine > pyridine > benzene)

P-44.2.1.2 The senior ring or ring system is a heterocycle [criterion (a) in P-44.2.1]. Example (the symbol > means ‘is senior to’):

	>
quinoline (PIN)		anthracene (PIN)

Examples (the symbol > means ‘is senior to’):

	>
1H-pyrrole (PIN)		2H-1-benzopyran (PIN) 2H-chromene
	>
1H-pyrrole (PIN)		2H-siline (PIN)

Examples (the symbol > means ‘is senior to’):

	>
furan (PIN)		thiophene (PIN)
[O > S]
	>
3a,7a-ethano-1-benzofuran (PIN)		1H,3H-3a,7a-ethano-2-benzothiophene (PIN)
[O > S]
	>
2-oxabicyclo[3.1.1]heptane (PIN)		1-phosphabicyclo[3.1.1]heptane (PIN)
[O > P]

Example (the symbol > means ‘is senior to’):

	>
isoquinoline (PIN)		1H-pyrrole (PIN)
[2 rings > 1 ring]

Examples (the symbol > means ‘is senior to’):

	>
quinoline (PIN)		1H-indole (PIN)
[10 skeletal atoms > 9 skeletal atoms]
	>
bicyclo[6.2.1]undecane (PIN)		naphthalene (PIN)
[11 skeletal atoms > 10 skeletal atoms]

	>
biphenylene (PIN)		1,4-methanonaphthalene (PIN)
[12 skeletal atoms > 11 skeletal atoms]

P-44.2.1.7 The senior ring or ring system has the greater number of heteroatoms of any kind [(criterion (f) in P-44.2.1]

Examples (the symbol > means ‘is senior to’):

(1)		>
	2,5,7-trioxabicyclo[4.1.1]octane (PIN)		2-oxabicyclo[4.1.1]octane (PIN)
	[3 heteroatoms > 1 heteroatom]
(2)		>
	cinnoline (PIN)		cyclopenta[c]azepine (PIN)
	[2 heteroatoms > 1 heteroatom]
(3)		>
	5,6,11,12-tetraoxadispiro[3.2.37.24]dodecane (PIN)		11-oxadispiro[3.1.36.34]dodecane (PIN)
	[4 heteroatoms > 1 heteroatom]
(4)		>
	silolo[3,4-c]silole (PIN)		cyclopenta[c]silole (PIN)
	[2 heteroatoms > 1 heteroatom]
(5)		>
	2H-6,8a-methanofuro[2,3-b]oxepine (PIN)		1H-3a,6-epoxyazulene (PIN)
	[2 heteroatoms > 1 heteroatom]

Examples (the symbol > means ‘is senior to’):

(1)		>
	pyrano[3,2-e][1,4]dioxepine (PIN)		3,1,5-benzoxadiphosphepine (PIN)
	[3 heteroatoms = 3 heteroatoms; 3 oxygen atoms > 1 oxygen atom]
(2)		>
	2,6,8-trioxa-7-stannaspiro[3.5]nonane (PIN)		2-oxa-6,7,8-trithiaspiro[3.5]nonane (PIN)
	[4 heteroatoms = 4 heteroatoms; 3 oxygen atom > 1 oxygen atom]
(3)		>
	spiro[[3,1]benzoxazine-4,1′-cyclopentane] (PIN)		4′H-spiro[cyclohexane-1,2′-cyclopenta[d][1,3]thiazine] (PIN)
	[2 heteroatoms = 2 heteroatoms] [1 nitrogen atom, 1 oxygen atom > 1 nitrogen atom, 1 sulfur atom]

P-44.2.2.1 Monocycles (see P-22)

If P-44.2.1 does not provide a decision, further criteria applicable to monocyclic rings are found in P-44.4.

P-44.2.2.2 Polycyclic systems. The senior polycyclic ring system occurs first in the following list of polycyclic ring system types:

The seniority order between parent hydrides having the same number of identical heteroatoms, the same number of rings, and the same number of skeletal atoms is a change from previous practice. Seniority of polycyclic ring systems is now facilitated by a hierarchical order of ring systems, which includes cyclic and acyclic phane systems and ranks all ring systems in the order given in this recommendation.

(a) spiro ring system (see P-24);

(b) cyclic phane system (see P-26);

(c) fused ring system (see P-25);

(d) bridged fused ring system (see P-25);

(e) nonfused bridged ring system (see P-23);

(f) linear phane system (see P-26);

(g) ring assembly (see P-28).

Further criteria applicable to polycyclic ring systems are found in P-44.4.

Examples (the symbol > means ‘is senior to’):

(1)		>
	8-azaspiro[4.5]decane (PIN)		quinoline (PIN)
	[spiro ring system (a) > fused ring system (c)]
(2)		>
	1,4(1,4)-dibenzenacyclohexaphane (PIN)		dibenzo[a,e][8]annulene (PIN)
	[cyclic phane ring system (b) > fused ring system (c)]
(3)		>
	naphthalene (PIN)		bicyclo[4.2.2]decane (PIN)
	[fused ring system (c) > nonfused bridged ring system (e)]
(4)		>
	benzo[8]annulene (PIN)		1,1′-biphenyl (PIN)
	[fused ring system (c) > ring assembly (g)]

(a) has the greater number of spiro fusions;

(b) consists of saturated monocyclic rings;

(c) consists of only discrete components.

P-44.2.2.2.1.1 The senior spiro system has the greater number of spiro fusions [criterion (a) in P-44.2.2.2.1].

Example (the symbol > means ‘is senior to’):

	>
6-azadispiro[4.2.48.25]tetradecane (PIN)		2′H-spiro[cyclopentane-1,1′-isoquinoline] (PIN)
[2 spiro fusions > 1 spiro fusion]

Example (the symbol > means ‘is senior to’):

	>
8,10-diazadispiro[3.1.56.14]dodecane (PIN)		5,11-diazadispiro[3.2.37.24]dodecane (PIN)
[saturated monocyclic rings each with 2 spiro fusions; the locant set for spiro fusions ‘4,6’ is lower that ‘4,7’]

P-44.2.2.2.1.3 The senior spiro system consists only of discrete components [criterion (c) in P-44.2.2.2.1] and:

(a) has the senior component determined by criteria above and below for the appropriate type of ring or ring system when the components are compared in their order of seniority; Example (the symbol > means ‘is senior to’):

	>
2′H-spiro[cyclopentane-1,1′-isoquinoline] (PIN)		spiro[indene-1,4′-piperidine] (PIN)
[isoquinoline > piperidine]

(b) has the senior component determined by criteria above and below for the appropriate kind of ring or ring system when compared in their order of citation in the name;

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1′-azadispiro[[1,3]dioxolane-2,2′-bicyclo[2.2.2]octane-5′,2′′-oxolane] (PIN) is senior to (II) 4-azadispiro[bicyclo[2.2.2]octane-2,2′-oxolane-3′,2′′-[1,3]dioxolane] (PIN) [first cited component dioxolane > bicyclo[2.2.2]octane]

(c) has the lower locant(s) for the spiro atoms in the order of citation in the name.

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1′H-spiro[cyclopentane-1,2′-quinoline] (PIN) is senior to (II) 2′H-spiro[cyclopentane-1,3′-quinoline] (PIN) [spiro fusion locant set 1,2′ in (I) is lower than 1,3′ in (II)]

The senior cyclic phane system:

(a) is the one occurring earlier in the following list of basic phane skeletal ring systems: spiro, von Baeyer, monocyclic;

(b) has the senior amplificant, as defined by P-44.2.1.2 through P-44.2.1.8;

(c) has the lower superatom locant(s) for all amplificants, first as a set compared term by term in order of increasing value and then in order of citation in the name;

(d) has the lower locant(s) for senior amplificants;

(e) has the lower set of attachment locants considered as a set when compared term by term in order of increasing numerical value;

(f) has the lower set of attachment locants when compared term by term in their order of citation in the name;

(g) has the lower locant(s) for heteroatoms introduced by skeletal replacement (‘a’) nomenclature without regard to kind;

(h) has the lower locant(s) for heteroatoms introduced by skeletal replacement (‘a’) nomenclature first cited in the following order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl.

P-44.2.2.2.2.1 The senior cyclic phane system occurs earlier in the following list of basic phane skeletal ring systems: spiro > nonfused bridged (von Baeyer) > monocyclic.

Examples (in order of decreasing seniority according to the criteria (a) in P-44.2.2.2.2):

4,12(1,3)-dibenzenaspiro[7.7]pentadecaphane (PIN)
(a spiro phane skeletal system)
is senior to

5,12(1,3)-dibenzenabicyclo[7.5.1]pentadecaphane (PIN)
(a von Baeyer phane skeletal system)
is senior to

1(1,3)-benzena-5(1,3)-cyclohexana-3(1,3)-cyclopentanacycloundecaphane (PIN)
(a monocyclic phane skeletal system)

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1(2,6)-pyrazina-6(1,3)-benzenacyclodecaphane (PIN) is senior to (II) 1,6(2,4)-dipyridinacyclodecaphane (PIN) [pyrazine > pyridine]

P-44.2.2.2.2.3 The senior cyclic phane system has the lower superatom locant(s) for all amplificants, first as a set compared term by term in order of increasing numerical value and then in order of their citation in the name [criterion (c) in P-44.2.2.2.2].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
1,4(1,3)-dibenzenacyclononaphane (PIN)		1,5(1,3)-dibenzenacyclononaphane (PIN)
[superatom locant set ‘1,4’ in (I) is lower than ‘1,5’ in (II)]

P-44.2.2.2.2.4 The senior cyclic phane system has the lower locants for senior amplificants [criterion (d) in P-44.2.2.2.2].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 3(3,5)-pyridina-1(1,3),6(1,4)-dibenzenacyclotridecaphane (PIN) is senior to (II) 6(2,5)-pyridina-1,3(1,3)-dibenzenacyclotridecaphane (PIN) [superatom locant ‘3’ for the senior amplificant pyridine is lower than ‘6’]

P-44.2.2.2.2.5 The senior cyclic phane system has the lower set of attachment locants considered as a set when compared term by term in order of increasing numerical value [criterion (e) in P-44.2.2.2.2].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
1,6(1,3)-dibenzenacyclodecaphane (PIN)		1(1,3),6(1,4)-dibenzenacyclodecaphane (PIN)
[the attachment locant set ‘(1,3)(1,3)’ is lower than ‘(1,3)(1,4)’]

P-44.2.2.2.2.6 The senior cyclic phane system has the lower set of attachment locants when compared term by term in their order of citation in the name [criterion (f) in P-44.2.2.2.2].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1,3,5,7(2,4)-tetrapyridinacyclooctaphane (PIN) is senior to (II) 1,5(2,4),3,7(4,2)-tetrapyridinacyclooctaphane (PIN) [the attachment locant set ‘(2,4)(2,4)(2,4)(2,4)’ is lower than ‘(2,4)(2,4)(4,2)(4,2)’]

P-44.2.2.2.2.7 The senior cyclic phane system has the lower locant(s) for heteroatoms specified by skeletal replacement (‘a’) prefixes without regard to kind [criterion (g) in P-44.2.2.2.2].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 3-oxa-2-thia-1,7(1,3)-dibenzenacyclododecaphane (PIN) is senior to (II) 5-oxa-2-thia-1,7(1,3)-dibenzenacyclododecaphane (PIN) [the heteroatom locant set ‘2,3’ is lower than ‘2,5’]

P-44.2.2.2.2.8 The senior cyclic phane system has the lower locant(s) for heteroatoms specified by skeletal replacement (‘a’) prefixes first cited in the following order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl [criterion (h) in P-44.2.2.2.2]. Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 2-oxa-3-thia-1,7(1,3)-dibenzenacyclododecaphane (PIN) is senior to (II) 3-oxa-2-thia-1,7(1,3)-dibenzenacyclododecaphane (PIN) [the locant ‘2’ for the senior heteroatom ‘O’ is lower than ‘3’]

P-44.2.2.2.3 Seniority criteria for fused ring systems given below are applied successively until no alternatives remain. The criteria are illustrated in P-44.2.2.2.3.1 through P-44.2.2.2.3.5. The senior fused ring system:

(a) has the larger individual ring component at first point of difference when their ring sizes are compared in order of decreasing size;

(b) has the greater number of rings in a horizontal row;

(c) has the lower letter(s) in the fusion descriptor when compared as a set; letters omitted in names are considered in the application of this criterion;

(d) has the lower number(s) in the fusion descriptor, in the order of appearance in the name; locants omitted in names are considered in application of this criterion;

(e) has the senior ring system component according to P-25.8 when its components are compared in order of decreasing seniority.

P-44.2.2.2.3.1 The senior fused ring system has the larger individual ring component at first point of difference when their ring sizes are compared in order of decreasing size [criterion (a) in P-44.2.2.2.3].

Example (the symbol > means ‘is senior to’):

	>
azulene (PIN)		naphthalene (PIN)
[the ring size ‘7’ in the ring set ‘7,5’ is larger than ‘6’ in the ring set ‘6,6’]

P-44.2.2.2.3.2 The senior fused ring system has the greater number of rings in a horizontal row [criterion (b) in P-44.2.2.2.3].

Example (the symbol > means ‘is senior to’):

(1)		>
	anthracene (PIN)		phenanthrene (PIN)
	[three rings in the horizontal row is greater than two]
(2)		>
	naphtho[1,2-g]quinoline (PIN)		naphtho[2,1-f]quinoline (PIN)
	[three rings in the horizontal row is greater than two]

Example (the symbol > means ‘is senior to’):

	>
5H-[1,3]dioxolo[4,5-c][1,2]oxaphosphole (PIN)		5H-[1,3]dioxolo[4,5-d][1,2]oxaphosphole (PIN)
[the letter ‘c’ in the fusion descriptor is lower alphabetically than ‘d’]

P-44.2.2.2.3.4 The senior fused ring system has the lower set of numbers in the fusion descriptor, in the order of appearance in a name; locants omitted in names are taken into consideration in application of this criterion [criterion (d) in P-44.2.2.2.3]. Example (the symbol > means ‘is senior to’):

	>
naphtho[1,2-f]quinoline (PIN)		naphtho[2,1-f]quinoline (PIN)
[the locant set ‘1,2’ in the fusion descriptor is lower than ‘2,1’]

P-44.2.2.2.3.5 The senior fused ring system has the senior ring system component according to P-25.8 when its components are compared in order of decreasing seniority [criterion (e) in P-44.2.2.2.3].

Example (the symbol > means ‘is senior to’):

	>
naphtho[2,3-f]quinoline (PIN)		naphtho[2,3-f]isoquinoline (PIN)
[the senior ring system quinoline is senior to isoquinoline (see P-25.2.1, Table 2.8)]

P-44.2.2.2.4 Seniority criteria for bridged fused ring systems given below are applied successively until no alternatives remain. The criteria are illustrated in P-44.2.2.2.4.1 through P-44.2.2.2.4.14. The senior bridged fused ring system:

(a) has the bridged ring system with the greater number of rings before bridging;

(b) is the bridged ring system with the greater number of ring atoms before bridging;

(c) is the bridged ring system with the fewer heteroatoms in the fused ring system before bridging;

(d) is the bridged ring system with the senior fused ring system before bridging according to P-44-2.2.2.3;

(e) has the lower set of locants for bridge attachments;

(f) has the lower locant(s) for heteroatoms in bridges, without regard to kind;

(g) has the lower locant(s) for heteroatoms in bridges, in the order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl;

(h) has the fewer composite bridges;

(i) has the fewer dependent bridges;

(j) has fewer atoms in dependent bridges;

(k) has the greater number of divalent bridges;

(l) has the lower set of locants for attachment of independent bridges;

(m) has the lower set of locants for attachment of dependent bridges;

(n) has the fused ring system with the greater number of noncumulative double bonds before bridging.

P-44.2.2.2.4.1 The senior bridged fused ring system has the bridged ring system with the greater number of rings before bridging [criterion (a) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
4,7-methanocyclopenta[a]indene (PIN)		2H-1,4:5,8-dimethanobenzo[7]annulene (PIN)
[three rings in the ring system before bridging is greater than two]

P-44.2.2.2.4.2 The senior bridged fused ring system is the bridged ring system with the greater number of ring atoms before bridging [criterion (b) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
1H-3,10a-methanophenanthrene (PIN)		1,4a-ethanofluorene (PIN)
[fourteen ring atoms in the ring system before bridging is greater than thirteen]

P-44.2.2.2.4.3 The senior bridged fused ring system is the bridged ring system with the fewer heteroatoms in the fused ring system before bridging [criterion (c) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
1,4:5,8-diepoxyanthracene (PIN)		1,4:6,9-dimethanooxanthrene (PIN)
[zero heteroatoms in the fused ring system before bridging is fewer than two]

P-44.2.2.2.4.4 The senior bridged fused ring system is the bridged ring system with the senior fused ring system before bridging according to P-44.2.2.2.3 [criterion (d) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
4,7-methanoazulene (PIN)		1,4-methanonaphthalene (PIN)
[azulene is senior to naphthalene, see P-44.2.1]

P-44.2.2.2.4.5 The senior bridged fused ring system has the lower set of locants for bridge attachments [criterion (e) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
1,3-methanonaphthalene (PIN)		1,4-methanonaphthalene (PIN)
[the locant set for bridge attachments ‘1,3’ is lower than ‘1,4’]

P-44.2.2.2.4.6 The senior bridged fused ring system has the lower locant(s) for heteroatoms in bridges, without regard to kind [criterion (f) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
5,1-(epoxyethano)octalene (PIN)		1,5-(methanooxymethano)octalene (PIN)
[the locant ‘13’ for the bridge oxygen atom is lower than ‘14’]

P-44.2.2.2.4.7 The senior bridged fused ring system has the lower locants for heteroatoms in bridges, in the order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl [criterion (g) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
5,1-(epoxymethanosulfano)octalene (PIN)		1,5-(epoxymethanosulfano)octalene (PIN)
[the locant ‘13’ for the senior oxygen atom in the bridge is lower than ‘15’]

P-44.2.2.2.4.8 The senior bridged fused ring system has the fewer composite bridges [criterion (h) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
1,4-epoxy-5,8-ethanonaphthalene (PIN)		1,4-(epoxymethano)-5,8-methanonaphthalene (PIN)
[zero composite bridges is fewer than one]

P-44.2.2.2.4.9 The senior bridged fused ring system has the fewer dependent bridges [criterion (i) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1,4-methano-10,13-pentanonaphtho[2,3-c][1]benzazocine (PIN) is senior to (II) 13,18-methano-6,10-pentanonaphtho[2,3-c][1]benzazocine (PIN) [zero dependent bridges is fewer than one]

P-44.2.2.2.4.10 The senior bridged fused ring system has fewer atoms in dependent bridges [criterion (j) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 13,18-methano-6,10-heptanonaphtho[2,3-c][1]benzazocine (PIN) is senior to (II) 13,18-ethano-6,10-hexanonaphtho[2,3-c][1]benzazocine (PIN) [one atom in the dependent bridge in (I) (atom 22) is fewer the two atoms in (II) (atoms 21 and 22)]

P-44.2.2.2.4.11 The senior bridged fused ring system has the greater number of divalent bridges [criterion (k) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 1-oxa-2,7:6,8-dimethanocycloocta[1,2,3-cd]pentalene (PIN) is senior to (II) 1-oxa-5,9,2-(ethane[1,1,2]triyl)cycloocta[1,2,3-cd]pentalene (PIN) [‘2’ divalent bridges in (I) is senior to the ‘1’ trivalent bridge in (II)]

P-44.2.2.2.4.12 The senior bridged fused ring system has the lower set of locants for attachment of independent bridges [criterion (l) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
(I) 13,18-methano-6,9-pentanonaphtho[2,3-c][1]benzazocine (PIN) is senior to (II) 13,18-methano-6,10-pentanonaphtho[2,3-c][1]benzazocine (PIN) [the locant set ‘6,9’ for the independent bridge in (I) is lower than the locant set ‘6,10’ in (II)]

P-44.2.2.2.4.13 The senior bridged fused ring system has the lower set of locants for attachment of dependent bridges [criterion (m) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
13,17-methano-6,10-pentanonaphtho[2,3-c][1]benzazocine (PIN) (I) is senior to 13,18-methano-6,10-pentanonaphtho[2,3-c][1]benzazocine (PIN) (II) [the locant set ‘13,17’ for the dependent bridge in (I) is lower than the locant set ‘13,18’ in (II)]

P-44.2.2.2.4.14 The senior bridged fused ring system has the fused ring system with the greater number of noncumulative double bonds before bridging [criterion (n) in P-44.2.2.2.4].

Example (the symbol > means ‘is senior to’):

	>
(I)		(II)
1,2,3,4,4a,9,9a,10-octahydro-9,10-ethanoanthracene (PIN) (I) is senior to 1,2,3,4,4a,8a,9,9a,10,10a-decahydro-9,10-ethenoanthracene (PIN) (II) [three noncumulative double bonds in (I) is greater than the two noncumulative double bonds in (II)]

P-44.2.2.2.5 Seniority criteria for bridged nonfused ring systems (von Baeyer ring systems) are applied successively until there are no alternatives remaining. These criteria are illustrated in P-44.2.2.2.5.1 through P-44.2.2.2.5.3. The senior bridged nonfused ring system:

(a) has the lower number at the first point of difference in the descriptor set for describing ring sizes when considered in order of citation in the name;

(b) has the lower set of bridge attachment locants (superscript locants) at the first point of difference when compared term by term in order of increasing numerical value;

(c) has the lower set of bridge attachment locants (superscript locants) at first point of difference when compared term by term in their order of citation in the name.

Further criteria applicable to bridged nonfused ring systems are found in P-44.4.

P-44.2.2.2.5.1 The senior bridged nonfused ring system has the lower number in the descriptor set for describing ring sizes at the first point of difference when considered in order of citation in the name [criteria (a) in P-44.2.2.2.5].

Example (the symbol > means ‘is senior to’):

	>
bicyclo[2.2.2]octane (PIN)		bicyclo[3.2.1]octane (PIN)
[the ring descriptor set ‘2,2,2’ is lower than ‘3,2,1’]

P-44.2.2.2.5.2 The senior bridged nonfused ring system has the lower set of bridge attachment locants (superscript locants) at the first point of difference when compared term by term in order of increasing numerical value [criteria (b) in P-44.2.2.2.5].

Example (the symbol > means ‘is senior to’):

	>
tricyclo[5.2.1.11,4]undecane (PIN)		tricyclo[5.2.1.12,5]undecane (PIN)
[the bridge attachment locant set ‘1,4’ is lower than ‘2,5’]

P-44.2.2.2.5.3 The senior bridged nonfused ring system has the lower set of bridge attachment locants (superscript locants) at first point of difference when compared term by term in their order of citation in the name [criterion (c) in P-44.2.2.2.5].

Example (the symbol > means ‘is senior to’):

	>
tetracyclo[5.5.2.22,5.18,12]heptadecane (PIN)		tetracyclo[5.5.2.22,6.18,12]heptadecane (PIN)
[the bridge attachment locant set ‘2,5,8,12’ is lower than ‘2,6,8,12’]

P-44.2.2.2.6 Linear (acyclic) phanes

Although linear phane systems can be viewed as heteroacyclic chains, in which the amplificants are heteroatoms and the connecting atoms or chains are carbon atoms, seniority for linear (acyclic) phanes follows closely the criteria used for cyclic phane systems (see P-44.2.2.2.2). Accordingly, the seniority criteria for linear phane systems given below are applied successively until no alternatives remain. These criteria are illustrated in P-44.2.2.2.6.1 through P-44.2.2.2.6.10. The senior linear phane system has:

(a) the senior amplificant, as defined by P-44.2.1.2 through P-44.2.1.8;

(b) most amplificants in their order of seniority as defined by P-44.2.1.2 through P-44.2.1.8;

(c) the maximum number of skeletal nodes;

(d) the lower superatom locant(s) for the senior amplificant;

(e) the lower superatom locant(s) for all amplificants as a set when compared term by term in order of increasing value and then in order of citation in the name;

(f) the lower superatom locant(s) for all amplificants when compared in order of citation in the name;

(g) the lower set of attachment locants considered as a set when compared term by term in order of increasing numerical value;

(h) the lower set of attachment locants when compared term by term in their order of citation in the name;

(i) the greater number of heteroatoms introduced by skeletal replacement (‘a’) nomenclature without regard to kind;

(j) the greater number of heteroatoms introduced by skeletal replacement (‘a’) nomenclature first cited in the following order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl.

P-44.2.2.2.6.1 The senior linear phane system has the senior amplificant, as defined by P-44.2.1.2. through P-44.2.1.8 [criterion (a) in P-44.2.2.2.6]

Examples:

(1)
	1(4)-pyridina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	is senior to
	1(4)-silina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	[the amplificant ‘pyridina’ is senior to the amplificant ‘silina’]
(2)
	1(2)-furana-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	is senior to
	1(2)-thiophena-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	[the amplificant ‘furana’ is senior to the amplificant ‘thiophena’]
(3)
	1(2)-quinolina-7(4)-pyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	is senior to
	1,7(4)-dipyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	[the amplificant ‘quinolina’ is senior to the amplificant ‘pyridina’]
(4)
	11H-1(2)-azepina-7(4)-pyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	is senior to
	1(2),7(4)-dipyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	[the amplificant ‘azepina’ is senior to the amplificant ‘pyridina’]

P-44.2.2.2.6.2 The senior linear phane system has the most amplificants in their order of seniority as defined by P-44.2.1.2 through P-44.2.1.8 [criterion (b) in P-44.2.2.2.6].

Examples:

(1)
	1,7(4)-dipyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	is senior to
	1(4)-pyridina-7(2)-silina-3,5(1,4)-dibenzenaheptaphane (PIN)
	[the amplificants ‘pyridina/pyridina’ are senior to the amplificants ‘pyridina/silina’]
(2)
	1(4)-cinnolina-7(4)-pyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	is senior to
	1(3)-quinolina-7(4)-pyridina-3,5(1,4)-dibenzenaheptaphane (PIN)
	[the amplificants ‘cinnolina/pyridina’ are senior to the amplificants ‘quinolina/pyridina’]
(3)
	1(4)-pyridina-7(2)-furana-3,5(1,4)-dibenzenaheptaphane (PIN)
	is senior to
	1(4)-pyridina-7(2)-thiophena-3,5(1,4)-dibenzenaheptaphane (PIN)
	[the amplificants ‘pyridina/furana’ are senior to ‘pyridina/thiophena’]

P-44.2.2.2.6.3 The senior linear phane system has the maximum number of skeletal nodes [criterion (c) in P-44.2.2.2.6]

Example:

1,10(1),3,5,7(1,4)-pentabenzenadecaphane (PIN)
is senior to

1,9(1),3,5,7(1,4)-pentabenzenanonaphane (PIN)
[the decaphane has more nodes than the nonaphane]

P-44.2.2.2.6.4 The senior linear phane system has the lower superatom locant(s) for the senior amplificants [criterion (d) in P-44.2.2.2.6].

Example:

1(4),7(2,5)-dipyridina-3,5(1,4),10(1)-tribenzenadecaphane (PIN)
is senior to

1(4),8(2,5)-dipyridina-3,5(1,4),10(1)-tribenzenadecaphane (PIN)
[the locant set ‘1,7’ for the pyridina amplificants is lower than the set ‘1,8’]

Example:

1,11(1),3,5,7(1,4)-pentabenzenaundecaphane (PIN)
is senior to

1,11(1),3,5,9(1,4)-pentabenzenaundecaphane (PIN)
[the locant set ‘1,3,5,7,11’ for the amplificants is lower than the set ‘1,3,5,9,11’]

Example:

1(4)-pyridina-7(2,5)-furana-9(2,5)-thiophena-3,5(1,4),11(1)-tribenzenaundecaphane (PIN)
is senior to

1(4)-pyridina-9(2,5)-furana-7(2,5)-thiophena-3,5(1,4),11(1)-tribenzenaundecaphane (PIN)
[the locant set for the amplificants in order of occurrence in
the name ‘1,7,9,3,5,11’ is lower than the locant set ‘1,9,7,3,5,11’]

Example:

1,7(1),3,5(1,3)-tetrabenzenaheptaphane (PIN)
is senior to

1,7(1),3(1,3),5(1,4)-tetrabenzenaheptaphane (PIN)
[the locant set ‘1,1,1,1,3,3’ for amplificant attachment locants in increasing numerical order is lower than ‘1,1,1,1,3,4’]

Example:

1(4)-pyridina-3(1,3),5(1,4),7(1)-tribenzenaheptaphane (PIN)
is senior to

1(4)-pyridina-3(1,4),5(1,3),7(1)-tribenzenaheptaphane (PIN)
[the locant set ‘4,1,3,1,4,1’ for the amplificant locants in order of their citation in the name is lower than ‘4,1,4,1,3,1’]

Example:

6-oxa-2-thia-1(4)-pyridina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
is senior to

2-thia-1(4)-pyridina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
[two heteroatoms intoduced by skeletal replacement (‘a’) nomenclature are senior to one such heteroatom]

Example:

2,10-dioxa-1,11(4)-dipyridina-3,5,9(1,4)-tribenzenaundecaphane (PIN)
is senior to

2-oxa-10-thia-1,11(4)-dipyridina-3,5,9(1,4)-tribenzenaundecaphane (PIN)
[two oxygen atoms are senior to one oxygen atom and one sulfur atom]

Example:

4-oxa-1(2),2,3(2,6)-tripyridina-5,6(1,4),7(1)-tribenzenaheptaphane (PIN)
1⁶-([1¹,2¹:2⁴,3¹]terphenyl]-1⁴-yloxy)-1²,2²:2⁶,3²-terpyridine;
[criteria for phane nomenclature (see P-52.2.5.1) are met for the PIN]

(a) rings containing any heteroatom;

(b) rings containing nitrogen;

(c) in the absence of nitrogen, rings containing at least one heteroatom first cited in the following sequence; F > Cl > Br > I > O > S > Se > Te > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl;

(d) the greater number of rings;

(e) the greater number of atoms;

(f) the greater number of heteroatoms of any kind;

(g) the greater number of heteroatoms first cited in the following sequence: F > Cl > Br > I > O > S > Se >Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl.

P-44.2.2.2.7.1 The senior ring assembly is composed of rings containing any heteroatom [criterion (a) in P-44.2.2.2.7].

Example (the symbol > means ‘is senior to’):

	>
2,2′-biphosphinine (PIN)		11,21:24,31-terphenyl (PIN) 1,1′:4′,1′′-terphenyl

Example (the symbol > means ‘is senior to’):

	>
2,2′-bipyridine (PIN)		2H,2′H-2,2′-bipyran (PIN)

Example (the symbol > means ‘is senior to’):

	>
2H,2′H-2,2′-bipyran (PIN)		2H,2′H-2,2′-bithiopyran (PIN)
[one oxygen atom per ring is preferred to one sulfur atom per ring]

Example (the symbol > means ‘is senior to’):

	>
2,2′-biquinoline (PIN)		12,22:25,32-terpyridine (PIN) 2,2′:5′,2′′-terpyridine
[a ring system consisting of two rings is senior to a ring system consisting of one ring]

Example (the symbol > means ‘is senior to’):

	>
1H,1′H-2,2′-biazepine (PIN)		2,4′-bipyridine (PIN)
[seven atoms per ring is preferred to six atoms per ring]

Example (the symbol > means ‘is senior to’):

	>
3,3′-bipyridazine (PIN)		2,3′-bipyridine (PIN)
[two heteroatoms per ring is preferred to one heteroatom per ring]

Example (the symbol > means ‘is senior to’):

	>
3,3′-bipyrano[3,2-e][1,4]dioxepine (PIN)		2,2′-bi-3,1,5-benzoxadiarsepine (PIN)
[three oxygen atoms per ring preferred to one oxygen atom per ring]

In an acyclic compound consisting of individual atoms, alike or different (an acyclic chain), the chain on which the nomenclature and numbering is based is called the ‘principal chain’. When there is a choice for the principal chain, the following criteria are applied, in the order listed, until a decision is reached.

The principal chain:

(a) contains the greater number of heteroatoms of any kind;

(b) has the greater number of skeletal atoms;

(c) contains the greater number of the most senior acyclic heteroatom in the following sequence: O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In >Tl.

Further criteria applicable to acyclic chains are found in P-44.4.

P-44.3.1 The principal chain contains the greater number of acyclic heteroatoms of any kind [criterion (a) in P-44.3].

Examples:

(1)
	2,5,8,11,14-pentaoxahexadecane (PIN)
	is senior to
	3,6,9,12-tetraoxaheptadecane (PIN)
	[five heteroatoms are greater than four]
(2)
	2,5,8,11,14-pentasilapentadecane (PIN)
	is senior to
	3,12-dioxa-6,9-dithiaheptadecane (PIN)
	[five heteroatoms are greater than four]

P-44.3.2 The principal chain has the greater number of skeletal atoms [criterion (b) in P-44.3].

In acyclic parent structures the order of seniority between unsaturation and length of chain given in earlier recommendations is reversed. Thus, the first criterion to be considered in choosing a preferred parent acyclic chain is the length of the chain; unsaturation is now the second criterion.

Example (the symbol > means ‘is senior to’):

(1)		>
	pentane (PIN)		butane (PIN)
	[five skeletal atoms is greater than four]
(2)		>
	pentasilane (preselected name; see P-12.2)		tetrasilane (preselected name; see P-12.2)
	[five skeletal atoms is greater than four)]
(3)		>
	octane (PIN)		hept-1-ene (PIN)
	[eight skeletal atoms is greater than seven]

(4)
	trideca-1,3-diene (PIN)
	is senior to
	octa-1,3,5,6-tetraene (PIN)
	[thirteen skeletal atoms is greater than eight]
(5)
	3,6,9,12-tetraoxapentadecane (PIN)
	is senior to
	3,6,9,12-tetraoxatetradecane (PIN)
	[four heteroatoms in each chain and fifteen skeletal atoms is greater than fourteen]
(6)
	2,5,8,11-tetrasilatridecane (PIN)
	is senior to
	tetrasilane (preselected name; see P-12.2)
	[four heteroatoms in each chain and thirteen skeletal atoms is greater than four]
(7)
	2,5,8,11,14-pentasilapentadecane (PIN)
	is senior to
	SiH3-O-SiH2-O-SiH3
	trisiloxane (preselected name; see P-12.2)
	[five heteroatoms in each chain; and fifteen skeletal atoms greater than five]

P-44.3.3 The principal chain contains the greater number of the most senior acyclic heteroatom in the order: O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In >Tl [criterion (c) in P-44.3].

Example (the symbol > means ‘is senior to’):

(1)
	2,5,8,11-tetraoxatridecane (PIN)
	is senior to
	2,5,8-trioxa-11-thiatridecane (PIN)
	[four oxygen atoms is more than three]

(2)	SiH3-O-SiH3	>	SiH3-S-SiH3
	disiloxane (preselected name; see P-12.2)		disilathiane (preselected name; see P-12.2)
	[oxygen is senior to sulfur]
(3)	SiH3-O-SiH3	>	SiH3-SiH2-SiH3
	disiloxane (preselected name; see P-12.2)		trisilane (preselected name; see P-12.2)
	[oxygen is senior to silicon]

P-44.4 SENIORITY CRITERIA APPLICABLE TO RINGS, RING SYSTEMS, OR ACYCLIC CHAINS

P-44.4.1 If the criteria of P-44.1 through P-44.3, where applicable, do not effect a choice of a senior parent structure, the following criteria are applied successively until there are no alternatives remaining. These criteria are illustrated in P-44.4.1.1 through P-44.4.1.12.

The senior ring, ring system, or principal chain:

(a) has the greater number of multiple bonds (P-44.4.1.1);

(b) has the greater number of double bonds (P-44.4.1.2);

(c) has one or more atoms with nonstandard bonding numbers (P-44.4.1.3);

(d) has the lower locants for indicated hydrogen (P-44.4.1.4);

(e) has the lower locants for heteroatoms introduced by skeletal replacement (‘a’) nomenclature as a set (P-44.4.1.5);

(f) has lower locants for heteroatoms introduced by skeletal replacement (‘a’) nomenclature in the order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl (P-44.4.1.6);

(g) has the lower locant(s) for carbon atoms at fusion sites (P-44.4.1.7);

(h) has the lower locant for an attached group expressed as a suffix (P-44.4.1.8);

(i) has the lower locants for points of attachment (if a substituent group) (P-44.4.1.9);

(j) has the lower locant(s) for endings or prefixes that express changes in the level of hydrogenation, i.e., for ‘ene’ and ‘yne’ endings and ‘hydro/dehydro’ prefixes (P-44.4.1.10);

(k) has one or more isotopically modified atoms (P-44.4.1.11);

(l) has one or more stereogenic centers (P-44.4.1.12).

Example (the symbol > means ‘is senior to’):

(1)		>		>
	benzene (PIN)		cyclohexene (PIN)		cyclohexane (PIN)
	[two double bonds greater than one double bond that is greater than zero]

(2)		>
	pent-3-en-1-yne (PIN)		pent-2-ene (PIN)
	[two multiple bonds greater than one]

(3)
	3,6,9,12-tetraoxatetradec-1-ene (PIN)
	is senior to
	3,6,9,12-tetraoxatetradecane (PIN)
	[one double bond greater than zero]
(4)
	1,10(1),4,7(1,4)-tetrabenzenadecaphan-2-en-8-yne (PIN)
	is senior to
	1,10(1),4,7(1,4)-tetrabenzenadecaphan-2-ene (PIN)
	[two multiple bonds senior to one multiple bond]
	or to
	1,10(1),4,7(1,4)-tetrabenzenadecaphan-2-yne (PIN)
	[one double bond senior to one triple bond]

Example (the symbol > means ‘is senior to’):

(1)		>
	cycloicosene (PIN)		cycloicosyne (PIN)
	[one double bond is senior to one triple bond]
(2)		>
	cycloicosa-1,8-diene (PIN)		cycloicos-1-en-3-yne (PIN)
	[two double bonds are senior to one double bond and one triple bond]
(3)		>
	1,4-dihydronaphthalene (PIN)		1,2,3,4-tetrahydronaphthalene (PIN)
	[four double bonds are greater than three]
(4)		>
	1,2,5,6-tetrasilacyclooct-3-en-7-yne (PIN)		1,2,5,6-tetrasilacycloocta-3,7-diyne (PIN)
	[one double bond and one triple bond is senior to two triple bonds since a double bond is senior to a triple bond]
(5)		>
	hepta-1,6-diene (PIN)		hept-1-en-6-yne (PIN)
	[two double bonds are senior to one double bond and one triple bond since a double bond is senior to a triple bond]

(6)
	1,10(1),4,7(1,4)-tetrabenzenadecaphane-2,8-diene (PIN)
	is senior to
	1,10(1),4,7(1,4)-tetrabenzenadecaphan-2-en-8-yne (PIN)
	[two double bonds are senior to one double bond and one triple bond since a double bond is senior to a triple bond]

P-44.4.1.3 The senior ring, ring system, or principal chain has one or more atoms with nonstandard bonding numbers [criterion (c) in P-44.4.1]. When choices are possible the following criteria are used in turn until a decision is reached.

P-44.4.1.3.1 When a choice is needed between two chains or between two rings or ring systems having skeletal atoms with nonstandard bonding numbers, the one having the maximum number of atoms with nonstandard bonding numbers is chosen as principal chain or senior ring or ring system. If a further choice is needed between the same skeletal atom with different nonstandard bonding numbers, preference for the senior parent structure is given in order of the decreasing numerical value of the bonding number, i.e., λ⁶ is senior to λ⁴.

Example (the symbol > means ‘is senior to’):

(1)		>
	1,3λ6-oxathiolane (PIN)		1,3λ4-oxathiolane (PIN)
	[the nonstandard bonding number λ6 is senior to λ4]
(2)		>
	1λ4,3λ5-thiaphospholane (PIN)		1λ4,3-thiaphospholane (PIN)
	[two nonstandard bonding atoms greater than one]
(3)		>
	2λ6-disilathiane (preselected name; see P-12.2)		disilathiane (preselected name; see P-12.2)
	[the nonstandard bonding number λ6 is senior to λ2]
(4)		>
	1λ5-diphosphane (preselected name; see P-12.2)		diphosphane (preselected name; see P-12.2)
	[the nonstandard bonding number λ5 is senior to λ3]

P-44.4.1.3.2 When a choice is needed between two chains or rings or ring systems having skeletal atoms with nonstandard bonding numbers, the one having the lowest locant(s) for (an) atom(s) with nonstandard bonding number(s) is chosen as principal chain or senior ring or ring system. If a further choice is needed, the one with the higher bonding number with the lowest locant is chosen.

Example (the symbol > means ‘is senior to’):

(1)		>
	1λ4-trisulfane (preselected name, see P-12.2)		2λ4-trisulfane (preselected name, see P-12.2)
	[the locant ‘1’ for the atom with the nonstandard bonding number is lower than ‘2’]
(2)		>
	1λ4,2,3-trithiane (PIN)		1,2λ4,3-trithiane (PIN)
	[the locant ‘1’ for the atom with the nonstandard bonding number is lower than ‘2’]
(3)		>
	1λ6,2λ4,3-trithiane (PIN)		1λ4,2λ6,3-trithiane (PIN)
	[the locant sets ‘1,2’ for the atoms with the nonstandard bonding number are the same,‘1,2’ but the superscript arabic number set giving the actual nonstandard bonding state is compared and the number set ‘6,4’ is senior to ‘4,6’]

P-44.4.1.4 The senior ring or ring system has the lowest locants for indicated hydrogen [criterion (d) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

(1)		>
	2H-pyran (PIN)		4H-pyran (PIN)
	[‘2H’ is lower than ‘4H’]

(2)
	72H-1(4),3,5(2,5)-tripyridina-7(2)-pyranaheptaphane (PIN)
	is senior to
	74H-1(4),3,5(2,5)-tripyridina-7(2)-pyranaheptaphane (PIN)
	[‘72H’ is lower than ‘74H’]

P-44.4.1.5 The senior ring, ring system, or principal chain has the lower locants for heteroatoms introduced by skeletal replacement (‘a’) nomenclature as a set [criterion (e) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

(1)
	1,7-dioxa-3,5-dithia-4-stannacycloundecane (PIN)
	is senior to
	1,9-dioxa-4,6-dithia-5-stannacycloundecane (PIN)
	[the heteroatom locant set ‘1,3,4,5,7’ is lower than ‘1,4,5,6,9’]
(2)
	1,4,6,10-tetraoxa-5λ5-phosphaspiro[4.5]decane (PIN)
	is senior to
	2,3,6,10-tetraoxa-5λ5-phosphaspiro[4.5]decane (PIN)
	[the heteroatom locant set ‘1,4,5,6,10’ is lower than ‘2,3,5,6,10’]
(3)
	2-oxa-5-thia-1,8(1),3,6(1,4)-tetrabenzenaoctaphane (PIN)
	is senior to
	2-oxa-7-thia-1,8(1),3,6(1,4)-tetrabenzenaoctaphane (PIN)
	[the heteroatom locant set ‘2,5’ is lower than ‘2,7’]

(4)		>
	1H-2,1,3-benzoxadisiline (PIN)		1H-2,1,4-benzoxadisiline (PIN)
	[the heteroatom locant set ‘1,2,3’ is lower than ‘1,2,4’]
(5)		>
	3,13-dioxabicyclo[8.2.1]tridecane (PIN)		4,13-dioxabicyclo[8.2.1]tridecane (PIN)
	[the heteroatom locant set ‘3,13’ is lower than ‘4,13’]

P-44.4.1.6 The senior ring, ring system, or principal chain has lower locants for heteroatoms introduced by skeletal replacement (‘a’) nomenclature in the order: F > Cl > Br > I > O > S > Se > Te > N > P > As > Sb > Bi > Si > Ge > Sn > Pb > B > Al > Ga > In > Tl [criterion (f) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

(1)		>
	1,2,3,4,5,7,6,8-hexathiaselenatellurocane (preselected name, see P-12.2)		1,2,3,4,6,7,5,8-hexathiaselenatellurocane (preselected name, see P-12.2)
	[the heteroatom locant set ‘1,2,3,4,5,7,6,8’ is lower than ‘1,2,3,4,6,7,5,8’]
(2)		>
	1,7,9-trioxa-2-azaspiro[4.5]decane (PIN)		2,7,9-trioxa-1-azaspiro[4.5]decane (PIN)
	[the heteroatom locant set ‘1,7,9,2’ in the order of their citation in the name is lower than ‘2,7,9,1’]
(3)		>
	4H,5H-pyrano[4,3-d][1,3,2]dioxathiine (PIN)		4H,5H-pyrano[4,3-d][1,2,3]dioxathiine (PIN)
	[the locant set ‘1,3,6’ for the senior oxygen atoms is lower than ‘2,3,6’]
(4)		>
	2-thia-4,6-diazabicyclo[3.2.0]heptane (PIN)		4-thia-2,6-diazabicyclo[3.2.0]heptane (PIN)
	[the locant ‘2’ for the senior sulfur atom is lower than ‘4’]

(5)
	2-oxa-5-thia-7-selena-1,8(1),3,6(1,4)-tetrabenzenaoctaphane (PIN)
	is senior to
	2-oxa-7-thia-5-selena-1,8(1),3,6(1,4)-tetrabenzenaoctaphane (PIN)
	[the ‘S’ atom > the ‘Se’ at locant number ‘5’]

P-44.4.1.7 The senior fused ring system has the lower locant(s) for carbon atoms at fusion sites [criterion (g) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

(1)		>		>
	aceanthrylene (PIN)		acephenanthrylene (PIN)		fluoranthene (PIN)
	(I)		(II)		(III)
	[the locant ‘2a’ for the fusion site in (I) is lower than ‘3a’ in (II) and the locant set ‘3a,5a’ for the fusion sites in (II) is lower than ‘3a,6a’ in (III)]

(2)		>
	chrysene (PIN)		triphenylene (PIN)
	[the locant set ‘4a,4b,6a’ for the fusion sites is lower than ‘4a,4b,8a’]

P-44.4.1.8 The senior ring, ring system, or principal chain has the lower locants for characteristic groups cited as a suffix [criterion (h) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

(1)		>
	pyridin-2(1H)-one (PIN)		pyridin-4(1H)-one (PIN)
	[the locant ‘2’ for the principal characteristic group is lower than ‘4’]

(2)
	octane-1,7-diol (PIN)
	is senior to
	octane-1,8-diol (PIN)
	[(the locant set ‘1,7’ for the principal characteristic group is lower than ‘1,8’]
(3)
	2,4,6,8-tetrasiladecane-1,9-diol (PIN)
	is senior to
	2,4,6,8-tetrasiladecane-1,10-diol (PIN)
	[the locant set for the principal characteristic group ‘1,9’ is lower than ‘1,10’]
(4)
	2,4-dioxa-1,7(1),3,5(1,4)-tetrabenzenaheptaphane-14,72-diol (PIN)
	is senior to
	2,4-dioxa-1,7(1),3,5(1,4)-tetrabenzenaheptaphane-14,74-diol (PIN)
	[the locant for the principal characteristic group ‘72’ is lower than ‘74’]

P-44.4.1.9 The senior ring or ring system has the lowest locants for points of attachment (if a substituent group) [criterion (i) in P-44.4.1].

Example (the symbol > means ‘is senior to’):

	>
pyridin-2-yl (preferred prefix)		pyridin-3-yl (preferred prefix)
[the locant for the point of attachment ‘2’ is lower than ‘3’]

P-44.4.1.10 The senior ring, ring system or principal chain has the lowest locants for endings or prefixes that express changes in the degree of hydrogenation, i.e., for ‘ene’ and ‘yne’ endings and ‘hydro/dehydro’ prefixes [criterion (j) in P-44.4.1].

The prefixes hydro or dehydro are introduced in names by an additive or subtractive operation; thus, they are not included in the category of alphabetizable detachable prefixes describing substitution (P-15.1.3). In names, they occupy a place between nondetachable prefixes and the alphabetizable detachable prefixes. The prefixes hydro or dehydro express modifications of the degree of hydrogenation of a ring or ring system having the maximum number of noncumulative double bonds (a mancude structure) and are treated for numbering like the endings ‘ene’ and ‘yne’, which fulfill the same function. In names, the prefix ‘dehydro’ precedes the prefix ‘hydro’, when both are present. Simple numerical terms, such as ‘di-’,‘tetra-’, etc., are used with ‘hydro’ and ‘dehydro’.

P-44.4.1.10.1 For the endings ‘ene’ and ‘yne’ lower locants are assigned first to the endings as a set without regard to type and then to ‘ene’ endings.

Example (the symbol > means ‘is senior to’):

(1)		>
	cycloicosa-1,3-dien-5-yne (PIN)		cycloicosa-1,7-dien-3-yne (PIN)
	[the locant set ‘1,3,5’ for the ‘ene’ and ‘yne’ endings is lower than ‘1,3,7’]
(2)		>
	cycloicosa-1,3-dien-5-yne (PIN)		cycloicosa-1,5-dien-3-yne (PIN)
	[the locant set ‘1,3’ for the ‘ene’ endings is lower than ‘1,5’]

(3)
	undeca-2,4-dien-7-yne (PIN)
	is senior to
	undeca-2,4-dien-8-yne (PIN)
	[the locant set ‘2,4,7’ for the ‘ene’ and ‘yne’ endings is lower than ‘2,4,8’]
(4)
	hexa-1,4-diene (PIN)
	is senior to
	hexa-1,5-diene (PIN)
	[the locant set ‘1,4’ for the ‘ene’ endings is lower than ‘1,5’]
(5)
	undeca-2,4,7-trien-9-yne-1,11-diol (PIN)
	is senior to
	undeca-2,4,9-trien-7-yne-1,11-diol (PIN)
	[the locant set ‘2,4,7’ for the ‘ene’ endings is lower than ‘2,4,9’]
(6)
	3,6,10,13-tetrathiahexadec-14-ene (PIN)
	is senior to
	3,6,10,13-tetrathiahexadec-15-ene (PIN)
	[the locant ‘14‘ for the ‘ene’ ending is lower than ‘15’]
(7)
	1,13(1),3,6,10(1,4)-pentabenzenatridecaphane-4-en-8-yne (PIN)
	is senior to
	1,13(1),3,6,10(1,4)-pentabenzenatridecaphan-4-en-11-yne (PIN)
	[the locant set ‘4,8’ for the ‘ene’ and ‘yne’ endings is lower than ‘4,11’]
(8)
	1,13(1),3(1,2),6,10(1,4)-pentabenzenatridecaphan-4,8-dien-11-yne (PIN)
	is senior to
	1,13(1),3(1,2),6,10(1,4)-pentabenzenatridecaphane-4,11-dien-8-yne (PIN)
	[the locant set ‘4,8’ for the ‘ene’ endings is lower than ‘4,11’]

Example (the symbol > means ‘is senior to’):

(1)		>
	1,2-dihydronaphthalene (PIN)		1,4-dihydronaphthalene (PIN)
	[the locant set for the ‘hydro’ prefixes ‘1,2’ is lower than ‘1,4’]

(2)
	11,12-dihydro-1(2)-quinolina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	is senior to
	11,14-dihydro-1(2)-quinolina-3,5(1,4),7(1)-tribenzenaheptaphane (PIN)
	[the locant set ‘11,12’ for the ‘hydro’ prefixes is lower than ‘11,14’)

(3)		>
	1,2-dihydrophosphinine (PIN)		1,4-dihydrophosphinine (PIN)
	[the locant set ‘1,2’ for the ‘hydro’ prefixes is lower than ‘1,4’]
(4)		>
	1,2,3,4-tetrahydrophosphinine (PIN)		2,3,4,5-tetrahydrophosphinine (PIN)
	[the locant set ‘1,2,3,4’ for the ‘hydro’ prefixes is lower than ‘2,3,4,5’]
(5)		>
	2,3-didehydropyridine (PIN)		3,4-didehydropyridine (PIN)
	[the locant set ‘2,3’ for the ‘dehydro’ prefixes is lower than ‘3,4’]

Criteria for choosing a preferred IUPAC name based on a senior parent structure as described in P-44 are found in P-45.

P-44.4.1.11 The senior ring, ring system, or principal chain that has one or more isotopically modified atoms [criterion (k) in P-44.4.1].

When there is a choice for the senior parent structure between isotopically modified and isotopically unmodified compounds or between isotopically modified compounds (see Chapter P-8), the senior parent structure is chosen according to the following criteria, applied successively until a decision can be made. In structures and names, nuclide symbols enclosed in parentheses describe isotopic substitution; nuclide symbols enclosed in square brackets describe isotopic labeling (see Chapter P-8).

P-44.4.1.11.1 The senior parent structure contains the greater number of isotopically modified atoms or groups.

Example (the symbol > means ‘is senior to’):

	>
(1-2H1)pentane (PIN)		pentane (PIN)
[one isotopically modified atom is senior to none]
	>
(1,1-2H2)cyclohexane (PIN)		(14C1)cyclohexane (PIN)
[two 2H atoms are senior to one 14C]

P-44.4.1.11.2 The senior parent structure has the greater number of nuclides of higher atomic number for modified atoms or groups.

Example (the symbol > means ‘is senior to’):

	>
(14C1)cyclopentane (PIN)		(2H1)cyclopentane (PIN)
[14C is senior to 2H]
	>
[1-14C]pentane (PIN)		[1-2H1]pentane (PIN)
[14C is senior to 2H]

P-44.4.1.11.3 The senior parent structure has the greater number of nuclides of higher mass number for modified atoms or groups.

Example (the symbol > means ‘is senior to’):

	>
(3H1)benzene (PIN)		(2H1)benzene (PIN)
[3H is senior to 2H]
	>
[1-14C]pentane (PIN)		[1-13C]pentane (PIN)
[14C is senior to 13C]

P-44.4.1.11.4 The senior parent structure has the lowest locant(s) for isotopically modified atoms or groups.

Example (the symbol > means ‘is senior to’):

	>
[4-2H1]pentanoic acid (PIN)		[5-2H1]pentanoic acid (PIN)
[4-2H is senior to 5-2H]
	>
(2-2H)pyridine (PIN)		(3-2H)pyridine (PIN)
[2-2H is senior to 3-2H]

P-44.4.1.11.5 The senior parent structure has the lower locant(s) for nuclides of higher atomic number for modified atoms or groups;

Example (the symbol > means ‘is senior to’):

	>
[4-13C,5-2H1]pentanoic acid (PIN)		[5-13C,4-2H1]pentanoic acid (PIN)
[4-13C is senior to 5-13C ]

P-44.4.1.11.6 The senior parent structure has the lowest locant(s) for nuclides of higher mass number for modified atoms or groups.

Example (the symbol > means ‘is senior to’):

	>
[4-13C,3-14C]butan-1-ol (PIN)		[3-13C,4-14C]butan-1-ol (PIN)
[3-14C is senior to 4-14C]

P-44.4.1.12 The senior ring, ring system, or principal chain has one or more stereogenic centers [criterion (l) in P-44.4.1].

P-44.4.1.12.1 ‘cis/trans’ Isomerism, the ‘E/Z’ convention

When there is a choice between parent structures that differ only by ‘Z’ and ‘E’ configurations, the senior parent structure contains the greater number of double bonds with ‘Z’ configuration; when a further choice is required, the senior parent structure has the lowest locant set for the double bond(s) with the ‘Z’ configuration. For the meaning of ‘Z’ and ‘E’ see Chapter P-9.

Example (the symbol > means ‘is senior to’):

(1)		>
	(Z)-cyclooctene (PIN) cis-cyclooctene		(E)-cyclooctene (PIN) trans-cyclooctene
	[‘Z’ is senior to ‘E’]
(2)		>
	(2Z)-2-methylbut-2-enoic acid (PIN)		(2E)-2-methylbut-2-enoic acid (PIN)
	[‘Z’ is senior to ‘E’]
(3)		>
	(4Z)-hex-4-enenitrile (PIN)		(4E)-hex-4-enenitrile (PIN)
	[‘Z’ is senior to ‘E’]

(4)
	(4Z,6E)-octa-4,6-dienoic acid (PIN)
	is senior to
	(4E,6E)-octa-4,6-dienoic acid (PIN)
	[‘Z,E’ is senior to ‘E,E’]
(5)
	(4Z,7E)-nona-4,7-dienoic acid (PIN)
	is senior to
	(4E,7Z)-nona-4,7-dienoic acid (PIN)
	[‘4Z,7E’ is senior to ‘4E,7Z’]

P-44.4.1.12.2 Enantiomerism, the ‘R’ and ‘S’ stereodescriptors

When there is a choice between parent structures differing only by the configurations of the chirality centers, the principal chain or the senior ring system is chosen by applying the CIP sequence rules 4 and 5, in the order: like stereodescriptors such as ‘RR’, ‘SS’ have priority over unlike ‘RS’ and ‘SR’ (‘l’ has priority over ‘u’), the ‘r’ over ‘s’, then ‘R’ over ‘S’. The CIP Sequence Rules are described in Chapter P-9.

Example (the symbol > means ‘is senior to’):

(1)
	(1R)-5′H-spiro[indene-1,2′-[1,3]oxazole] (PIN)
	is senior to
	(1S)-5′H-spiro[indene-1,2′-[1,3]oxazole] (PIN)
	[‘R’ is senior to ‘S’]
(2)
	(5R,7R)-1,8-dioxadispiro[4.1.47.25]tridecane (PIN)
	is senior to
	(5R,7S)-1,8-dioxadispiro[4.1.47.25]tridecane (PIN)
	[‘RR’ is senior to ‘RS’]

P-44.4.1.12.3 ‘cis/trans’ Isomerism (the ‘E/Z’ convention) and enantiomerism (the ‘R/S’ convention)

When there is a choice between parent structures that contain both ‘E/Z’ (or cis/trans) and ‘R/S’ descriptors the ‘E/Z’ (or cis/trans) descriptors are preferred to the ‘R/S’ descriptors.

Example

	>
(2R,3Z)-2-hydroxypent-3-enoic acid		(2S,3E)-2-hydroxypent-3-enoic acid

[Z is senior to E]

P-45 SELECTION OF PREFERRED IUPAC NAMES

P-45.0 INTRODUCTION

Two or more names may result based on the same senior parent structure selected according to P-44, because of different substitution patterns or multiple occurrences of the same senior parent structure. A parent structure is defined (P-15.1) as a parent hydride, for example, benzene, a functionalized parent hydride, for example cyclohexanol, or a functional parent compound, for example, acetic acid. Application of the criteria in this section will generate the preferred IUPAC name.

P-45.1 Multiplication of identical senior parent structures
P-45.2 Criteria related to number and location of substituent groups
P-45.3 Criteria related only to substituents with nonstandard bonding numbers, other criteria being equal
P-45.4 Criteria related only to isotopic modification of substituents
P-45.5 Criteria related to alphanumerical order of names
P-45.6 Criteria related only to configuration

P-45.1.1 Multiplicative nomenclature is senior to substitutive nomenclature for generating preferred IUPAC names to express multiple occurrences of identical senior parent structures, other than alkanes, in the name of the parent structure (see P-51.3.1). In most cases multiplicative names are shorter than regular substitutive names. A preferred IUPAC name is generated by multiplicative nomenclature when the following criteria for its use are met (see P-51.3.1).

(1) the linking bonds (single or multiple) between the central substituent group of the multiplicative group and all subsequent structural units are identical; and

(2) the multiplicative groups, other than the central multiplicative group, are symmetrically substituted; and

(3) the locants of all substituent groups on the identical parent structures, including suffix groups, are identical.

Example:

4,4′-oxybis(2-chlorobenzoic acid) (PIN, multiplicative name)
but

4-(4-carboxy-2-chlorophenoxy)-2-chlorobenzoic acid (PIN, substitutive name)

Examples:

1,1′-[(phenylmethylene)bis(sulfanediylmethylene)]dibenzene (PIN)
(multiplication of three benzene rings is not possible)

2,2′,2′′,2′′′-(ethane-1,2-diyldinitrilo)tetraacetic acid
N,N′-(ethane-1,2-diyl)bis[N-(carboxymethyl)glycine]

4,4′,4′′-(ethene-1,1,2-triyl)trianiline (PIN)
[not 4,4′-[2-(4-aminophenyl)ethene-1,1-diyl]dianiline;
the PIN multiplies three parent structures;
the second name multiplies only two]

[phosphanetriyltris(methylene)]tris(phosphonic acid) (PIN)

1,1′,1′′-({[(diphenylmethyl)sulfanyl]diphenylmethoxy}methanetriyl)tribenzene (PIN)
(not 1,1′-({[diphenyl(triphenylmethoxy)methyl]sulfanyl}methylene)dibenzene;
the PIN multiplies three parent structures;
the second name multiplies only two)

The following criteria are applied, in turn, until a decision is reached. The preferred IUPAC name is the name based on the senior parent structure that has:

P-45.2.1 the maximum number of substituent groups cited as prefixes;
P-45.2.2 the lower locant set for substituent groups cited as prefixes;
P-45.2.3 the lower locant set for substituent groups in order of citation in the name

Examples:

(1)
	4-methoxy-N-phenylaniline (PIN) [not N-(4-methoxyphenyl)aniline; the PIN parent structure has more substituents, two simple substituents vs. one compound substituent]
(2)
	4-chloro-2-[(3-cyanophenyl)methyl]benzonitrile (PIN) [not 3-[(5-chloro-2-cyanophenyl)methyl]benzonitrile; the PIN parent structure has more substituents, two (one simple and one complex) substituents vs. one complex substituent]
(3)
	1-methyl-4-(phenoxymethyl)benzene (PIN) [not [(4-methylphenyl)methoxy]benzene; the PIN parent structure has more substituents; two (one simple and one compound) substituent vs. one complex substituent]
(4)
	N,N,2-trimethyl-3-{4-methyl-3-[2-methyl-3-(methylamino)-3-oxopropyl]phenyl}propanamide (PIN) [not 3-{5-[(3-dimethylamino)-2-methyl-3-oxopropyl]-2-methylphenyl}-N,2-dimethylpropanamide; the PIN parent structure has more substituents, four (three simple and one complex) substituents vs. three (two simple and one complex)]
(5)
	13-chloro-2-(naphthalen-2-yl)-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane (PIN) [not 2-(3-chloronaphthalen-2-yl)-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane; the PIN parent structure has more substituents, two simple substituents vs. one compound substituent]
(6)
	1,1-dimethyl-3-{[(1λ4-thian-3-yl)sulfanyl]methyl}-1λ4-thiane (PIN) [not 3-{[(1,1-dimethyl-1λ4-thian-3-yl)methyl]sulfanyl}-1λ4-thiane; the PIN parent structure has more substituents, three (two simple and one complex) substituents vs. one complex substituent]
(7)
	3-ethyl-2-methylhexane (PIN) [not 3-isopropylhexane or 3-(propan-2-yl)hexane; the PIN parent structure has more substituents, two simple substituents vs. one simple substituent)
(8)
	6-methyl-4-propylheptanoic acid (PIN) [not 4-(2-methylpropyl)heptanoic acid; the principal chain has more substituent, two simple substituents vs. one compound substituent]
(9)
	4-bromo-2-[3-(bromomethyl)pent-1-en-2-yl]-4-methyl-3-methylidenehexanoic acid (PIN) [not 4-(bromomethyl)-2-(3-bromo-3-methylpent-1-en-2-yl)-3-methylidenehexanoic acid; the PIN parent chain has more substituents; four (three simple and one complex) substituents vs. three (one simple and two compound)] 4-bromo-2-[2-(bromomethyl)-1-methylidenebutyl]-4-methyl-3-methylidenehexanoic acid
(10)
	2-(disilanyldisulfanyl)-1,1,1-trimethyldisilane (PIN) [not [2-(2,2,2-trimethyldisilanyl)disulfan-1-yl]disilane; the PIN parent structure has more substituents, four (three simple and one compound) substituents vs. one complex substituent]
(11)
	3-disilanyl-2-silylhexasilane (preselected name, see P-12.2) [not 3-(trisilan-2-yl)hexasilane or 3-(1-silyldisilanyl)hexasilane; the PIN parent chain has more substituents, two simple substituents vs. one simple or one compound substituent]
(12)
	4-[4-carboxy-3-(λ6-sulfanyl)phenoxy]-2-phosphanyl-3-(λ6-sulfanyl)benzoic acid (PIN) [not 4-[4-carboxy-3-phosphanyl-2-(λ6-sulfanyl)phenoxy]-2-(λ6-sulfanyl)benzoic acid) the PIN parent structure has more substituents, three (two simple and one compound) substituents vs. two (one simple and one complex)]
(13)
	5-(81Br)bromo-3-[1-(81Br)bromopropyl]-4-methylhexanoic acid (PIN) [not 4-(81Br)bromo-3-[3-(81Br)bromobutan-2-yl]hexanoic acid; the PIN parent chain has more substituents, three (two simple and one compound) vs. two (one simple and one compound)]

P-45.2.2 The preferred IUPAC name is based on the senior parent structure that has the lower locant or set of locants for substituents cited as prefixes (other than ‘hydro/dehydro’) to the parent structure.

Examples:

(1)
	2-(2-amino-4-methylphenoxy)-N-methylaniline (PIN) [not 5-methyl-2-[2-(methylamino)phenoxy]aniline; the locant set ‘N,2’ in the PIN is lower than ‘2,5’]
(2)
	1-bromo-3-chloro-6-nitro-2-[2-(1,3,7-trifluoronaphthalen-2- yl)ethyl]naphthalene (PIN) [not 2-[2-(1-bromo-3-chloro-6-nitronaphthalen-2-yl)ethyl]-1,3,7-trifluoronaphthalene; the locant set ‘1,2,3,6’ in the PIN is lower than ‘1,2,3,7’]
(3)
	3,3′-[bis(4-carboxyphenyl)methylene]dibenzoic acid (PIN) [not 4,4′-[bis(3-carboxyphenyl)methylene]dibenzoic acid; the locant set 3,3′ in the PIN is lower than 4,4′]
(4)
	11-bromo-2-(4-chloronaphthalen-2-yl)-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane (PIN) [not 2-(1-bromonaphthalen-2-yl)-14-chloro-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane; the locant set ‘11,2’ in the PIN is lower than the locant set ‘14,2’]
(5)
	3-[5-(3-amino-2-methyl-3-oxopropyl)-2-methylphenyl]-N-methylpropanamide (PIN) [not 2-methyl-3-{4-methyl-3-[3-(methylamino)-3-oxopropyl]phenyl}propanamide; the locant set ‘N,3’ in the PIN is lower than ‘2,3’]
(6)
	5,6-dibromo-4-(1-chloro-3-nitropropyl)heptanoic acid (PIN) [not 5-chloro-4-(1,2-dibromopropyl)-7-nitroheptanoic acid; the locant set ‘4,5,6’ in the PIN is lower than ‘4,5,7’]
(7)
	2-amino-5-(2-chloro-4-hydroxybutyl)-6-methylnonane-1,9-diol (PIN) [not 2-amino-7-chloro-5-(5-hydroxypentan-2-yl)nonane-1,9-diol; not 5-(3-amino-4-hydroxybutyl)-3-chloro-6-methylnonane-1,9-diol; the locant set ‘2,5,6’ in the PIN is lower than the locant set ‘2,5,7’ or ‘3,5,6’]
(8)
	5-methyl-4-(2-methylprop-1-en-1-yl)hepta-1,5-diene (PIN) [not 4-(but-2-en-2-yl)-6-methylhepta-1,5-diene; the locant set ‘4,5’ in the PIN is lower than ‘4,6’]
(9)
	5-bromo-3-[3-nitro-1-(λ5-phosphanyl)propyl]-4-(λ5-phosphanyl)hexanoic acid (PIN) [not 3-[2-bromo-1-(λ5-phosphanyl)propyl]-6-nitro-4-(λ5-phosphanyl)hexanoic acid, the locant set ‘3,4,5’ in the PIN is lower than the locant set ‘3,4,6’]
(10)
	4-(4-carboxy-2-phosphanylphenoxy)-2-(λ5-phosphanyl)benzoic acid (PIN) [not 4-[4-carboxy-3-(λ5-phosphanyl)phenoxy]-3-phosphanylbenzoic acid; the locant set ‘2,4’ in the PIN is lower than ‘3,4’]
(11)
	4-[4-carboxy-2-(λ4-sulfanyl)phenoxy]-2-(λ6-sulfanyl)benzoic acid (PIN) [not 4-[4-carboxy-3-(λ6-sulfanyl)phenoxy]-3-(λ4-sulfanyl)benzoic acid; the locant set ‘2,4’ in the PIN is lower than ‘3,4’]
(12)
	4-(4-carboxy-2-phosphanylphenoxy)-2-(λ6-sulfanyl)benzoic acid (PIN) [not 4-[4-carboxy-3-(λ6-sulfanyl)phenoxy]-3-phosphanylbenzoic acid; the locant set ‘2,4’ in the PIN is lower than ‘3,4’]
(13)
	3-{[3-(2H2)amino-5-methylcyclohexa-1,5-dien-1-yl]sulfanyl}-2- methylcyclohexa-2,4-dien-1-(2H2)amine (PIN) [not 3-{[3-(2H2)amino-2-methylcyclohexa-1,5-dien-1-yl]sulfanyl}-5-methylcyclohexa-2,4-dien-1-(2H2)amine, the locant set ‘2,3’ in the PIN is lower than ‘3,5’]
(14)
	4-(81Br)bromo-3-[2-(81Br)bromopropyl]hexanoic acid (PIN) [not 5-(81Br)bromo-3-[1-(81Br)bromopropyl]hexanoic acid, the locant set in the PIN, ‘3,4’ is lower than ‘3,5’]
(15)
	3-chloro-5-(3-hydroxybutyl)-4,6-dimethylnonane-2,8-diol (PIN) [not 7-chloro-5-(3-hydroxybutyl)-4,6-dimethylnonane-2,8-diol: the locant set of the PIN is ‘3,4,5,6’ which is lower than ‘4,5,6,7’]

P-45.2.3 The preferred IUPAC name is based on the senior parent structure that has the lower locant or set of locants for substituents cited as prefixes to the parent structure (other than ‘hydro/dehydro’ prefixes) in their order of citation in the name.

Examples:

(1)
	3-chloro-7-[(4-chloro-3-nitroquinolin-7-yl)sulfanyl]-4-nitroquinoline (PIN) [not 4-chloro-7-[(3-chloro-4-nitroquinolin-7-yl)sulfanyl]-3-nitroquinoline, the locant sets are the same in both names, i.e., ‘3,4,7’, but in their order of appearance in the name the locant set ‘3,7,4’ in the PIN is lower than ‘4,7,3’]
(2)
	2-bromo-N-(4-bromo-2-chlorophenyl)-4-chloroaniline (PIN) [not 4-bromo-N-(2-bromo-4-chlorophenyl)-2-chloroaniline; the locant sets are the same, i.e., ‘N,2,4’, but in their order of appearance in the name the locant set ‘2,N,4’ in the PIN is lower than ‘4,N,2’]
(3)
	1-ethyl-7-[(7-ethyl-8-propylnaphthalen-2-yl)oxy]-2-propylnaphthalene (PIN) [not 2-ethyl-7-[(8-ethyl-7-propylnaphthalen-2-yl)oxy]-1-propylnaphthalene, the locant sets are the same in both names, i.e., ‘1,2,7’, but in their order of appearance in the name, the locant set in the PIN ‘1,7,2’ is lower than ‘2,7,1’]
(4)
	5-bromo-4-(2-bromo-1-fluoropropyl)-6-fluoroheptanoic acid (PIN) [not 6-bromo-4-(1-bromo-2-fluoropropyl)-5-fluoroheptanoic acid; the locant sets are the same in both names, i.e., ‘4,5,6’, but in their order of appearance in the name the locant set ‘5,4,6’ in the PIN is lower than ‘6,4,5’]
(5)
	3-bromo-2-(2-bromo-1-hydroxyethyl)-4-hydroxybutanoic acid (PIN) [not 4-bromo-2-(1-bromo-2-hydroxyethyl)-3-hydroxybutanoic acid; the locant sets are the same in both names, i.e., ‘2,3,4’, but in their order of appearance in the name, the locant set ‘3,2,4’ in the PIN is lower than ‘4,2,3’]
(6)	(I)
	11-ethyl-8-(4-ethyl-3-methylhex-5-en-1-yl)-12-methyltetradeca-1,3,13-triene (PIN) (I) (II) [not 12-ethyl-8-(3-ethyl-4-methylhex-5-en-1-yl)-11-methyltetradeca-1,3,13-triene (II) the locant sets are the same in both names, i.e., ‘8,11,12’, but in their order of appearance in the name the locant set ‘11,8,12’ in the PIN is lower than ‘12,8,11’]
(7)
	2-(2-bromoethyl)-4-chlorobutan-1-ol (PIN) [not 4-bromo-2-(2-chloroethyl)butan-1-ol the locant sets are the same in both names, i.e., ‘2,4’ but in the order of appearance in the name, the locant set ‘2,4’ in the PIN is lower than ‘4,2’]
(8)
	1-bromo-5-(bromomethyl)-1,6-dichlorohexane (PIN) [not 1,6-dibromo-1-chloro-5-(chloromethyl)hexane; the locant sets are the same in both names, i.e., ‘1,1,5,6’ but in their order of appearance in the name, the locant set ‘1,5,1,6’ is lower than ‘1,6,1,5’]
(9)
	7-ethyl-6-(3-ethylpent-4-en-2-yl)-8-methyldeca-1,3,9-triene (PIN) not 8-ethyl-7-methyl-6-(4-methylhex-5-en-3-yl)deca-1,3,9-triene [the locant sets are the same in both names, i.e. ‘6,7,8’ but in their order of appearance in the name, the locant set ‘7,6,8’ is lower than ‘8,7,6’]
(10)
	N-methyl-3-{4-methyl-3-[3-oxo-3-(propylamino)propyl]phenyl}propanamide (PIN) [not 3-{2-methyl-5-[3-(methylamino)-3-oxopropyl]phenyl}-N-propylpropanamide; the locant sets are the same in both names, i.e. ‘N,3’ but in their order of appearance in the name, the locant set ‘N,3’ in the PIN is lower than ‘3,N’]
(11)
	3-[2-bromo-1-(λ5-phosphanyl)propyl]-5-chloro-4-(λ5-phosphanyl)hexanoic acid (PIN) [not 5-bromo-3-[2-chloro-1-(λ5-phosphanyl)propyl]-4-(λ5-phosphanyl)hexanoic acid; the locant sets are the same in both names, i.e. ‘3,4,5’ but in their order of appearance in the name, the locant set ‘3,5,4’ in the PIN is lower than ‘5,3,4’]
(12)
	4-(81Br)bromo-3-[1-(81Br)bromo-2-bromopropyl]-5-chlorohexanoic acid (PIN) [not 4-(81Br)bromo-5-bromo-3-[1-(81Br)bromo-2-chloropropyl]hexanoic acid; the locant sets are the same in both names, i.e. ‘3,4,5’ but in their order of appearance in the name, the locant set ‘4,3,5’ in the PIN is lower than ‘4,5,3’]
(13)
	5-butyl-8-ethyl-3-methyl-6-propyldecane (PIN) [not 6-butyl-3-ethyl-8-methyl-5-propyldecane; both have the set of locants ‘3,5,6,8’ but the PIN has them in the order ‘5,8,3,6’ which is lower than ‘6,3,8,5’]
(14)
	1-ethyl-6-[(8-ethyl-5-propylnaphthalen-2-yl)selanyl]-4-propylnaphthalene (PIN) [not 4-ethyl-6-[(5-ethyl-8-propylnaphthalen-2-yl)selanyl]-1-propylnaphthalene: both have the locant set ‘1,4,6’ but the PIN set is in the order ‘1,6,4’ which is lower than ‘4,6,1’]
(15)
	1,5-dibromo-4-(2-bromo-1-iodoethyl)-1,6-dichlorohexane (PIN) [not 1,6-dibromo-4-(1-bromo-2-chloroethyl)-1-chloro-5-iodohexane; both have the locant set ‘1,1,4,5,6’ but the PIN set is in the order ‘1,5,4,1,6’ which is lower than ‘1,6,4,1,5’]

P-45.3 CRITERIA RELATED ONLY TO SUBSTITUENTS WITH NONSTANDARD BONDING NUMBERS, OTHER CRITERIA BEING EQUAL

The following criteria are relative only to substituents with nonstandard bonding numbers applied in turn, until a decision is reached, earlier criteria having been satisfied.

P-45.3.1 the maximum number of substituent group(s) with the higher bonding number cited as prefixes;
P-45.3.2 the lower locant set for substituent group(s) with the higher bonding number cited as prefixes.

Examples:

3-(λ⁵-phosphanyl)-2-(phosphanylmethyl)propanoic acid (PIN)
[not 3-phosphanyl-2-(λ⁵-phosphanylmethyl)propanoic acid;
the PIN parent structure contains the substituent group having the highest bonding number, ‘λ⁵’ > ‘λ³’]

4-(2λ⁵-diphosphan-1-yl)-2-(2-diphosphanylethyl)butanenitrile (PIN)
[not 4-diphosphanyl-2-[2-(2λ⁵-diphosphan-1-yl)ethyl]butanenitrile;
the PIN parent structure contains the substituent group having the highest bonding number, ‘λ⁵’ > ‘λ³’]

3-(λ⁶-sulfanyl)-2-(λ⁴-sulfanylmethyl)propanoic acid (PIN)
[not 3-(λ⁴-sulfanyl)-2-(λ⁶-sulfanylmethyl)propanoic acid;
the PIN parent structure contains the substituent group having the highest bonding number, ‘λ⁶’ > ‘λ⁴’]

Example:

5-(1λ⁵-diphospan-1-yl)-2-[3-(2λ⁵-diphospan-1-yl)propyl]pentanoic acid (PIN)
[not 5-(2λ⁵-diphospan-1-yl)-2-[3-(1λ⁵-diphospan-1-yl)propyl]pentanoic acid]
The locant ‘1λ⁵’ for the nonstandard bonding number directly bonded to the parent structure is lower than ‘2λ⁵’.

The following criteria are relative only to substituents with isotopic modification applied in turn, until a decision is reached, earlier criteria having been satisfied.

P-45.4.1 The preferred IUPAC name is based on the senior parent structure that has the lowest locant(s) for isotopically modified substituent groups.

Example:

2-bromo-1-{[2-(⁸¹Br)bromopentyl]oxy}pentane (PIN)
[not 2-(⁸¹Br)bromo-1-[(2-bromopentyl)oxy]pentane]
The isotopically modified substituent for the PIN is attached at ‘1’ which is lower than ‘2’.

Example:

2-(¹³C)methoxy-N-[2-(¹⁸O)methoxyethyl]ethan-1-amine (PIN)
[not 2-(¹⁸O)methoxy-N-[2-(¹³C)methoxyethyl]ethan-1-amine]
¹⁸O > ¹³C; the ¹⁸O isotopically modified substituent for the PIN is attached at ‘N’ which is lower than ‘2’.

Example:

4-[2-¹³C]ethyl-2-(2-[2-¹⁴C]ethylpentyl)heptan-1-ol (PIN)
[not 4-[2-¹⁴C]ethyl-2-(2-[2-¹³C]ethylpentyl)heptan-1-ol
¹⁴C > ¹³C; the ¹⁴C isotopically modified substituent for the PIN is attached at ‘2’ which is lower than ‘4’

The preferred IUPAC name is the name that is earlier in alphanumerical order (see P-14.5). Alphabetic letters are considered first in the order that they appear in the name; all Roman letters are considered before any italic letters, unless the latter are used as locants or are a part of a compound or composite locant, for example, ‘N’ and ‘4a’. Then, if still there is a choice, numerical locants are considered in the order of their appearance in the name.

Examples:

(1)
	1-bromo-4-chloro-2-{2-[(1,4-dibromonaphthalen-2-yl)methoxy]ethyl}naphthalene (PIN) [not 1,4-dibromo-2-{[2-(1-bromo-4-chloronaphthalen-2-yl)ethoxy]methyl}naphthalene; in both names the locant set is ‘1,2,4’, and the locants appear in the name in the same order ‘1,4,2’ so no decision can be made by P-45.2.2 or P-45.2.3; but ‘bromo’ in the PIN is earlier alphabetically than ‘dibromo’.]
(2)
	2-bromo-4-chloro-N-(2,4-dibromophenyl)aniline (PIN) [not 2,4-dibromo-N-(2-bromo-4-chlorophenyl)aniline; ‘bromo’. in the PIN is earlier alphabetically than ‘dibromo’.]
(3)
	13-bromo-14-chloro-2-(3,4-dibromonaphthalen-2-yl)-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane (PIN) [not 13,14-dibromo-2-(3-bromo-4-chloronaphthalen-2-yl)-1(2)-naphthalena-3,5(1,4),7(1)-tribenzenaheptaphane; ‘bromo’ in the PIN is earlier alphabetically than ‘dibromo’.]
(4)
	4-(1,2-difluoropropyl)-5,6-dinitroheptanoic acid (PIN) [not 4-(1,2-dinitropropyl)-5,6-difluoroheptanoic acid; ‘difluoro’ in the PIN is earlier alphabetically than ‘dinitro’]
(5)
	5-(81Br)bromo-3-[3-(81Br)bromobutan-2-yl]-4-nitrohexanoic acid (PIN) [not 5-(81Br)bromo-3-[2-(81Br)bromo-1-nitropropyl]-4-methylhexanoic acid; ‘bromo-bromo-butanyl’ is lower alphanumerically than ‘bromo-bromo-nitro’] [Note: The ‘B’ of the element symbol ‘Br’ is not a factor in the alphabetization]