NUCLEAR MAGNETIC RESONANCE STUDIES OF BONDING IN AROMATIC SYSTEMS . A CORRELATION OF HAMMETT SIGMA CONSTANTS WITH METHYL C13-H COUPLING CONSTANTS AND CHEMICAL SHIFTS

Methyl C18-H coupling constants were measured for a series of substituted toluenes, t-butylbenzenes, N,N-dimethylanilines, and anisoles. A linear relationship between coupling constants and Hammett σ constants of substituents was found, and the relative slopes of these lines (toluenes > dimethylanilines > anisoles > t-butyl-benzenes) were interpreted in terms of the mode of transmission of substituent effects to the methyl site. Methyl chemical shifts also exhibit a linear correspondence to the σ constants, with a slightly different order of relative slopes (toluenes > anisoles ⋝ dimethylanilines > t-butylbenzenes). The use of σ* values for those substituents capable of direct resonance interactions in the dimethylanilines and anisoles greatly improved the linear consistency of the correlations for these series. © 1969, American Chemical Society. All rights reserved.