Alkane Distribution as Biological Markers: Presence and Possible Origin of n-Alkanes in Guttiferae Heartwoods

THE thin waxy materials coating the stem, leaf, flower and fruit of most plants usually consist of homologous series of long chain alcohols, aldehydes, esters and hydrocarbons. The hydrocarbons contain a homologous series of n-alkanes ranging from about C20 to C35 with the alkanes having an odd number of carbon atoms sometimes occurring ten times more abundantly than those with an even number. The centre of the distribution of the series is frequently around the n-alkanes C29 and C31 (ref. 1). These features are also obvious in some hydrocarbons from fossils and it has been suggested that this predominance of n-alkanes with an odd number of carbon atoms can be used to indicate that the hydrocarbons are of biological origin1. For petroleum, which does not have this distribution of n-alkanes, Robinson has proposed that the hydrocarbons arise from partly biological and partly non-biological sources1,2. More recent work has shown that lower organisms such as mosses, algae and lichens contain n-alkanes where the ratio of odd-numbered homologues to the even-numbered ones is about equal and it was suggested that crude oils may originate from lower organisms3.