Ab Initio Calculations of the Relative Strengths of the π Bonds in Acetylene and Ethylene and of Their Effect on the Relative Energies of π-Bond Addition Reactions

Abstract

Energies at the CI-SD/6-31G* level have been calculated for acetylene, ethylene, ethane, and the vinyl and ethyl anions, radicals, and cations (classical and hydrogen-bridged). From these energies, the differences between the π-bond energies in acetylene and ethylene and between the energies of addition of H−, H*, H+, and H2 to these π bonds have been computed. Also reported are the calculated differences between the ionization potentials and between the electron affinities of the vinyl and ethyl radicals and between the energies required for formation of vinyl and ethyl anions, radicals, and cations from, respectively, ethylene and ethane. Excellent agreement is found between the calculated energies differences and those derived from the most recent experimental data. The differences between the energies of addition reactions to the π bonds in acetylene and in ethylene are analyzed, and the effect of the nonlinear geometry of vinyl radical on the π-bond energy of acetylene is discussed. © 1991, American Chemical Society. All rights reserved.