A theoretical(PCILO) study of hydrogen bonding in carboxylic acids and their adducts with pyridine

Abstract

The perturbative configuration interaction using localized orbitals (PCILO) method was used for the study of the hydrogen bond in open and cyclic dimers of formic, acetic and propionic acids, The calculations, in agreement with experimental evidence, have shown that cyclic dimers of tree carboxylic acids studied are more stable than their respective open dimers. In the case of formic acid the open tri-, tetra- and pentamers were also studied and the stabilization energy per hydrogen bond becomes practically constant when the number of bonds exceeds four. The PCILO calculations of the systems carboxylic acid - pyridine have shown that O-H…N bonds with energy of about 50 kJ mole−1 are more stable than those O-H…O in carboxylic acid dimers. The complexes (formic acid)2 Py and (formic acid)2 (Py)2 were also studied. Calculated H-bonded arid 0-H stretching force constants were found to be higher than available ab initio and experimental values.