Continued from LG-2 Modified Parent Structures
The parent structures described in LG-1 and LG-2 have the maximum number of non-cumulative double bonds in the rings corresponding to C-1 to C-6 and C-1' to C-6', and saturated side chains. Methods for describing changes from this skeletal oxidation level depend on the location of the modification.
LG-3.1 Unsaturation in the Side Chain
The presence of a double bond (or triple bond) in the side chain (i.e. C-7 to C-9 and C-7' to C-9') of the lignane, neolignane or epoxyneolignane skeleton is indicated by changing the -ane ending to -ene (or -yne) with a locant to indicate the position of the double bond. If there are two double bonds then the -ane ending is changed to -diene with retention of the 'a'.
LG-3.2 Reduction of the Aromatic Ring
If an aromatic ring is reduced the location of the additional hydrogen atoms is indicated by the prefix dihydro (or tetrahydro, etc) with the appropriate locants. See also LG-4 for saturation due to the presence of a ketone.
LG-3.3 Double Bonds Between the Aromatic Ring and Side Chain
Isomerisation of a double bond from the aromatic ring to the adjacent atom in the side chain is indicated by reduction of the aromatic ring using dihydro (or tetrahydro), see LG-3.2, followed by didehydro with the appropriate locants of the new double bond.