Hydrogen bonding in organic compounds. II. Amine-cabonyl interactions

Abstract

A comparison of the infra-red spectra of typical aromatic compounds, with a primary amine group adjacent to a carbonyl group, with the spectra of related compounds, shows that, in the former, weak hydrogen bonding occurs between the two groups. The strength of the bonds formed is in the order : 1-aminoanthraquinone > 2-amino-acetophenone > methyl anthranilate, and the changes in carbonyl frequency are comparable with those of the symmetric NH2 stretching frequency. Stronger hydrogen bonds are formed in corresponding ortho-acetamido compounds. A brief study of the NH2 stretching frequencies of o-nitroamines in dioxan solution shows that there is considerable interaction between solute and solvent but this cannot be definitely attributed to intermolecular hydrogen bonding.