Ab initio calculations on some binary systems involving hydrogen bonds

Molecular conformation studies on the binary systems acetonitrile-water, acetonitrile-methanol, acetonitrile-hydrogen cyanide, formamide-water, formamide-methanol and methanol-hydrogen cyanide have been carried out by ab initio methods at STO 3-21G, 4-31G and 6-31G levels. Calculations on the monomer units have also been performed at the same levels. The total energies, interaction energies and dipole moments are calculated for all the conformers. Nuclear quadrupole coupling constants (NQCCs) are calculated theoretically by evaluating the electric field gradient (EFG) at the site of the nitrogen nucleus for the formamide and acetonitrile complexes by the procedure of Kaplansky and Whitehead (Trans. Faraday Soc., 65 (1969) 641). The NQCCs are found to be practically the same for both cyclic and linear structures in each case, but the cyclic structure is more energetically favoured than the linear structure in the case of the formamide complexes and the linear structure is preferred to the cyclic structure in the case of the acetonitrile complexes. The energy calculation study on the methanol-hydrogen cyanide complex favours an asymmetric linear structure. © 1995.