Capillary gas chromatography of alkylbenzenes II. Correlations between the structures and methylene group increments and differences in retention indices of isomers

The contribution to gas chromatographic retention behaviour of methylene group increments and differences in the retention indices (dI) of isomers of alkylbenzenes up to C16 on squalane and acetyltri-n-butyl citrate was studied. The methylene group increments appear to vary over a wide range (60–100 i.u.) and depend on the magnitude, positions and relative lengths of the alkyl chains and on the number of carbon atoms. Anomalous retention behaviour of n-propylbenzene and its derivatives, except for molecules in which there are alkyl groups in both positions vicinal to the n-propyl group, was found. Hence, the correlations of ICH2 in homologous series can serve as indicators of fine structural peculiarities of the molecules. The applicability of regularities in methylene group increments and dI values, based on precise measurements of retention indices of low-molecular-weight alkylbenzenes, for confirmation of the identities of high-molecular-weight alkylbenzenes ( > C10) is demonstrated