Nuclear magnetic resonance study of cis–trans-isomerism in some N-alkylformamides and N-alkylacetamides and their O-protonated cations in anhydrous acids

Abstract

cis–trans-Isomerism has been observed in the n.m.r. spectra (at 90 MHz and 27 °C) of the O-protonated cations of N-alkylformamides (alkyl = Me, Et, or Pr¹), N-methylacetamide, and the corresponding NN-dimethyl derivatives in 100% sulphuric acid, pure fluorosulphuric acid, and 72% perchloric acid. The spectra of the unprotonated amides in water and deuteriochloroform have also been recorded for comparison. The isomer ratios have been determined and the effect of O-protonation on the chemical shifts and the coupling constants discussed.