ABSTRACT
Many aliphatic hydrocarbons are found in plants, the most common being long-chain nalkanes with the general formula H3C -(CH 2)n-C H r The lowest natural member of straightchain alkanes is n-pentane, although its higher homologue n-heptane is more common. The series of plant n-alkanes extends to C35 and it is noteworthy that the odd-numbered members are much more abundant than are the even-numbered. This fact is apparently related to their pathway of synthesis which involves decarboxylation of fatty acids with even numbers of carbon atoms. Branched hydrocarbons are also found, usually in small quantities. Branching commonly occurs near the end of the chain (methyl group in the b-1-2801-30-done ω-1 or ω-2 positions). Many branchedchain hydrocarbons are acyclic terpenoids. These are based on the isoprene molecule and are therefore (C5)n-compounds. Although there is no reason to believe that the pathways and mechanisms involved in the mammalian metabolism of these terpenoid compounds differ significantly from those involved in the metabolism of other compounds containing similar chemical groups, terpenoids are grouped separately in this book. A further type of aliphatic hydrocarbon from plants includes compounds containing unsaturated groups. Olefinic groups are most common, however a few hydrocarbons containing acetylenic groups are also known.
