The mechanism of addition to a CN triple bond. An ab initio study of the first stages of the Stephen, Gatterman and Houben-Hoesch reactions

Abstract

The mechanism of addition of HCl to the triple bond of RCN (R=H, CH,) is studied by means of ab initio SCF and CI calculations. Geometries and energies of minima (initial H-bonded complexes, products) and saddle points (transition state) are completed by a determination of the intrinsic reaction coordinate and of a relatively large portion of the energy hypersurface. The evolution of the electronic structure along the reaction coordinate is interpreted using localized orbitals. Particular attention is paid to the effect of chemical substitution, for which a new test, based on the electrostatic forces acting on nuclei along the reaction coordinate, has been employed. CI calculations performed over canonical and localized orbitals are compared to determine whether the latter formulation is more convenient for non-equilibrium geometries.