Correlations of Alkybenzene Structures with Mass Spectra

Correlations of alkylbenzene structures with mass spectra show clearly that structural features determine the products of dissociation by electron impact. The most-abundant ions derive from cleavage of bonds β to the benzene ring. Increase in length of side-chains promotes: (a) decomposition of the parent ion, (b) cleavage of carbon-carbon bonds in competition with carbon-hydrogen bonds, (c) cleavage of β bonds in competition with a bonds, and (d) hydrogen migration accompanying bond cleavage. Side-chain branching, number, and position on the benzene ring help fix the product distribution. The factors that govern dissociation of alkylbenzenes apply broadly to the dissociation of other arenes and related heterocyclic compounds. A scheme for the identification of alkylbenzenes, based upon the correlations, has proved effective in analyzing samples that did not yield readily to other techniques.