Substituent effects on the N.M.R. spectra of carboxylic acid derivatives. II. ³H N.M.R. spectra of substituted benzamides and N-alkylbenzamides

Abstract

The tritium n.m.r. spectra of 12 substituted benzamides and five series of N-alkylbenzamides have been measured, after tritiation of the amides, and the chemical shifts, δ_N3H, have been compared with δ_NH. The values correlate well when σ_R(BA) is substituted in the Taft DSP equation. Good correlations are also obtained with the Hammett σ parameter. The non-equivalence of the two amido protons of benzamides, arising from the barrier to rotation round the carbon-nitrogen bond, has been confirmed by use of triton n.m.r. spectroscopy.