Substituent effects on methyl proton chemical shifts in substituted phenyltrimethylsilanes and tert-butylbenzenes

Abstract

The chemical shifts of methyl protons in six mono-substituted phenyltrimethylsilanes and in thirteen tert-butylbenzenes have been determined at infinite dilution in carbon tetrachloride. Electron-releasing groups lead to an increase in shielding of the methyl protons of their trimethylsilyl or tert-butyl groups, whereas electron withdrawing groups decrease this shielding. Good correlations exist between the chemical shifts of the methyl protons and the Hammett σ constants for both series of compounds. The Hammett ϱ values were found to be −5.86 and −5.38 (in cps/σ) for phenyltrimethylsilanes and tert-butylbenzenes, respectively.