INTRAMOLECULAR O-H-CENTER-DOT-CENTER-DOT-N HYDROGEN-BONDS IN 2-HYDROXYBENZALDIMINE COMPOUNDS - SPECTROSCOPIC AND QUANTUM-CHEMICAL INVESTIGATIONS

Spectroscopic and quantum chemical data that characterize the intramol ecular hydrogen bonds in a series of 2-hydroxybenzaldimine compounds ( Ph(OH)(CH=N-R); R = -NH(Ph), -OH, -OCH3, -NH2, -Ph, -CHO, -H, -CH3, -( CO)(CH3) are reported. Optimized geometries and vibrational spectra we re calculated at HF/6-31G(d,p) and B3LYP/6-31G(d,p) levels, NMR spectr a at GIAO-BLYP/6-311++G(d,p)//B3LYP/6-31G(d, level of theory. The sequ ences of calculated frequencies (nu(OH) and nu(CN)) and chemical shift s (delta(OH)) agree reasonably well with the corresponding experimenta l data. The consistency of the calculated data is demonstrated by expl oiting several correlations between bond distances, vibrational freque ncies, chemical shifts, and hydrogen bond energies. In particular, the re exists an almost perfect relation between the hydrogen bond strengt hs, as measured by r(O-H) distances, and the hydrogen bond distances r (H .. N) and r(O .. N). It is shown that electrostatic potentials and several kinds of partial charges (Mulliken, CHELPG, MK, and NPA) of th e nitrogen atoms, to a first approximation, may serve as a means for c haracterizing the proton acceptor capabilities of the different imino groups.