The retention index system applied to alkylbenzenes and monosubstituted derivatives

Summary

The additivity concept in the retention index system of Kovats has been examined for a series ofn-alkylbenzenes and theiro- andp-monosubstituted nitro-, amino-, and chloro-derivatives. Anomalous behaviour is exhibited by the first three members of the series on both polar and non-polar stationary phases. For addition of a methylene group ton-propylbenzene or ap-substituted derivative, it is found that the retention increment, Δl CH₂, approaches 100 units. However, the strong inductive effect of the group in the ortho position and the steric effects apparent in ano-substituted alkylbenzene lead to large variations of retention increment upon addition of-CH₂-to the alkyl chain.

A study ofn-alkylbenzene retention on Apiezon L and Carbowax 20M over a wide range of temperatures has verified the linearity of the retention increment with temperature and has revealed that this gradient increases with increasing carbon side-chain length for the first few members of the series, thereafter becoming constant. Functional retention increments, Δl_x, for substitution of nitro-, amino- and chloro-groups into the benzene ring are given.