Vibrational study of intramolecular hydrogen bonding in o-hydroxybenzoyl compounds

The vibrational study of a set of o-hydroxybenzoyl compounds (salicylaldehy de, o-hydroxyacetophenone, methyl salicylate and salicylamide) and their pa rent compounds (phenol, benzaldehyde, acetophenone, methyl benzoate and ben zamide) has been performed by infrared (IR) measurements and by quantum che mical calculations using B3LYP density functional in conjunction with 6-31G * * and 6-311 + + G(3df, 2p) basis sets. The assignment of the infrared ba nds results unequivocal for most cases, including those signals in which th e motion of the intramolecular hydrogen bond (IMHB) is involved. The analys is of the IR spectra for the deuterated derivatives was proved to be a very useful tool for this purpose. A model based on isotopically substituted be nzenes was used for classifying the phenyl ring movements of the molecules studied. The results obtained show the suitability and limitation of the ha rmonic treatment using B3LYP method to describe the characteristic IMHB vib rations. Vibrational data are analyzed in order to obtain information about the nature of the hydrogen bonding interaction in this family of compounds . Finally, the available empirical relationships to approximate the IMHB en ergy from experimental spectroscopic data are revised in view of the new th eoretical results. (C) 1999 Elsevier Science B.V. All rights reserved.