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.