Determining the stability of three-carbon carbocations and carbanions through computing ionization energies, electron affinities and frontier molecular orbital energy gaps for corresponding radicals, cations and anions

Complete basis set ab initio computational studies were performed on three-carbon anions, radicals and cation isomers with the aim being to evaluate their relative stabilities. As a measure of the stability of the carbocations, adiabatic ionization energies for corresponding radicals were computed, while in the evaluation of the relative stability of carbanions, the electron affinities of radicals were used. The reliability of the complete basis set ab initio method for computing those values, as well as using the ionization energies for determining the stabilities of the cations and using the electron affinities for determining the stabilities of carbanions were all discussed. To determine the relative stabilities in the three-carbon series of cations and anions their frontier orbital energy gaps were computed. The frontier molecular orbital energy gaps were compared with the CBSQ energies and the reliability of this approach for the evaluation of the chemical system stability was discussed. (C) 2000 Elsevier Science B.V. All rights reserved.