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Lignans and neolignans are a large group of natural products characterized by the coupling of two C₆C₃ units. For nomenclature purposes the C₆C₃ unit is treated as propylbenzene and numbered from 1 to 6 in the ring, starting from the propyl group, and with the propyl group numbered from 7 to 9, starting from the benzene ring. With the second C₆C₃ unit the numbers are primed. When the two
C₆C₃ units are linked by a bond between positions 8 and 8′ the compound is referred to and named as a lignan. In the absence of the C-8 to C-8′ bond, and where the two C₆C₃ units are linked by a carbon–carbon bond it is referred to and named as a neolignan. The linkage with neolignans may include C-8 or C-8′.
Where there are no direct carbon–carbon bonds between the C₆C₃ units and they are linked by an ether oxygen atom the compound is named as an oxyneolignan.
The nomenclature provides for the naming of additional rings and other modifications following standard organic nomenclature procedures for naming natural products. Provision is included to name the higher homologues. The sesquineolignans have three C₆C₃ units, and dineolignans have four C₆C₃ units.

Pure & Appl. Chem., Vol. 72, No. 8, p. 1493–1523, 2000
© 2000 IUPAC
IUPAC permission is acknowledged