Ab initio studies of electron acceptor-donor interactions with blue- and red-shifted hydrogen bonds

The features of blue- and red-shifted-electron acceptor-donor (ACH/B) hydrogen bonds have been compared by using quantum chemical calculations. The geometry, the interaction energy and the vibrations frequencies of blue- (ACH = F3CH, Cl3CH with B = FCD3) and red-shifted (ACH - F3CH, Cl3CH with B = NH3 and ACH = CH3CCH with B = FCD3, NH3) complexes were obtained by using ab initio MP2(Full)/6-31 + G(d,p) calculations with the a priori basis-set superposition error (BSSE) correction method. One-dimensional potential energy and dipole moment functions of the dimensionless normal coordinate Q(1), corresponding to the CH stretching mode of ACH, have been compared for both types of complexes. Contributions of separate components of the inter-action energy to the frequency shift and the effect of electron charge transfer were examined for a set of intermolecular distances by using the symmetry-adapted perturbation theory (SAPT) approach and natural bond orbitals (NBO) population analysis.