Theoretical investigations on the hydrogen bonding of nitrile isomers with H2O, HF, NH3 and H2S

The hydrogen bonds formed by the interaction of nitriles with water, hydrogen fluoride, ammonia and hydrogen sulphide have been studied using B3LYP and second-order MOller-Plesset perturbation (MP2) methods and 6-311+ +G(d,p) basis set. The energies and structures of 80 hydrogen-bonded complexes between nitriles and small molecules were examined systematically using B3LYP and MP2 procedure. Categorisation of the hydrogen bonds involved in the various complexes led to an ordering of hydrogen bond donor and acceptor abilities for some functional groups. The interaction energies have been corrected for the basis set superposition error using Boy's counterpoise correction method. The Morokuma energy decomposition analysis reveals that the strong interactions are due to the attractive contributions from the electrostatic (ES), polarisation (PL) and charge transfer (CT) components. The topological parameters, electron density and Laplacian of electron density show excellent correlation with the hydrogen bond length. Natural bond orbital (NBO) analysis has also been performed to study the CT from proton acceptor to the antibonding orbital of the H-Y bond in the proton donor part of complexes. The frequency analysis of C-H...Y bond in the complexes indicates the blue-shifting nature largely in case of sp(2) hybridised carbon atom.