Nuclear magnetic resonance studies of internal rotation—III Rotational barriers in <i>META</i>‐ and <i>PARA</i>‐substituted <i>N</i>, <i>N</i>‐dimethylcinnamamides

Abstract

Abstract The rotational barriers about the CN bond of eight m ‐ and p ‐substituted N , N ‐dimethyl cinnamamides have been determined by the iterative total line shape NMR method. The ΔG values have been correlated with the substituent constants σ, σ n and σ + . By comparison of the results with literature data, some conclusions about the accuracy of the barrier determination as well as the transmittance of polar effects in conjugated amides have been drawn.