Specificity of the intramolecular hydrogen bond. The differences in spectroscopic characteristics of the intermolecular and intramolecular H-bonds

摘要

IR spectroscopic properties-positions of nu(OH) bands and their integrated intensities for series of nine Schiff bases, 16 complexes of phenols with N, N-dimethylbenzylamine and 11 complexes of phenols with N-benzylidenemethylamine-were determined in CCl4 solutions and compared with their Delta pK(a) values. Characteristics of particular groups of compounds with the hydrogen bond were determined. It was shown that the strong decrease of the intensity of the nu(OH) bands is a specific feature of the intramolecular hydrogen bonding in comparison to related intermolecular complexes. It results from bending of the intramolecular hydrogen bond and is not limited to pseudoaromatic chelate rings only. Such conclusion results also from semiempirical and ab initio calculations. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 24]