Diastereotopic effect of the methylene protons in N-ortho-substituted-N-β-cyanoethylanilides: X-ray structure of N-(β-cyanoethyl)-2′-chloromaleanilic acid

Abstract

Some N-β-cyanoethyl-ortho-substituted anilides show a diastereotopic coupling effect of the methylene protons of the N-β-cyanoethyl chain in the 1H n.m.r. spectra. Resolution of those proton coupling systems have been done by computational methods and their analyses indicate that in chloroform solution the gauche conformation is preferred in all those compounds. The solid-state X-ray analysis of (2) also shows that this is in a special gauche conformation. The diasterotopic effect can be seen as restricted rotational freedom of the alkyl chain in ortho-substituted compounds. However, an internal linkage between an N-α-proton of the chain and the CO amide group seems to be the common anchorage of the α-methylene, while the β-methylene protons are fixed by steric and dipole effects.