Electronic effects of halogen-substituted methyl groups

Abstract

The electronic effects of the halogen-substituted methyl groups, CH_nX_3-n, where X is F, Cl, Br or I, have been examined by ¹³C n.m.r, spectroscopy in a series of α-halogen-substituted toluenes. The substituent chemical shifts of all carbon atoms, as well as the σ_I and σ_R⁰ substituent parameters derived from a dual substituent parameter (DSP) analysis, are examined in terms of hyperconjugative and π-inductive substituent effects. Bulky CH_nX_3-n substituents cause molecular deformations of the benzene ring, consequently invalidating the derivation of substituent parameters from a DSP analysis.