Page 19 - Pharmd general phytochemistry I-Final2024_LEUCTERS

The isoprene rule:
The carbon skeletons of terpenes can be built up by the union of two or
more isoprene (isopentene) residues. These units are usually united in a
head-to-tail manner.

Terpenes thus are made up of two, three, four, six or eight C5 units.
each isoprene unit contains two double bonds, but one disappears for
each pair that is connected.

The main classification of terpenes is on the basis of the number of
isoprene units in the molecule, a single "terpene unit" being equal to two
isoprene units:

Isoprene units Cn Group
2 C 10 Monoterpenes
3 C 15 Sesquiterpenes
4 C 20
6 C 30 Diterpenes
8 C 40 Triterpenes
>8 C > 40 Tetraterpenes
PoIyterpenes

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