On the suitability of AM1 for the modeling of molecules containing amino groups

Abstract

The molecular structures of conjugated amines calculated on the semi-empirical level and determined experimentally via X-ray crystallography, are compared. AM1 is superior to PM3 in reproduction of experimental geometries of amino groups attached to the π-acceptors and gives better results for strong acceptors than for weak ones. For the former, an account for the medium effect (e.g. using COSMO) is necessary. For the medium-strong acceptors, the AM1-COSMO calculations exaggerate systematically the non-planarity of amino group. Only few examples of significant (in terms of energy) distinctions between experimental and calculated geometries of amino groups were found, among them: nitrogen-containing heterocycles and the derivatives of 1-aminoanthraquinone.