Effect of 3p Atomic Orbital on Energy of the Double Bond

Abstract

The energy of the π—π part of the double bond is calculated by (1) the perturbation method using the ``united atom'' model, and (2) the MO method where the wave function used is constructed as a linear combination of atomic orbitals, as a function of internuclear distance. In each case the wave function includes the 3p atomic orbital. The results of the investigation indicate (1) that the wave function ordinarily used in the MO method is not appreciably improved by the inclusion of the 3p atomic orbital, and (2) that the absolute value of the energy calculated by the MO method using p functions centered at the nuclei, is at least 20 percent too low at the distances occurring in the C–C bond.