Computational study of the singlet cyclopropenyl and triplet cyclopropynyl cations aromatic stabilization with Petersson's complete basis set ab initio approach

Abstract

An extensive computational study of three-carbon hydrocarbon neutral and carbocation isomers were investigated with Petersson's complete basis set ab initio methods with the aim being to evaluate stabilization through conjugation, as well as through aromatization. Several approaches were used, varying from comparison of the MP2/6-31G(d′) computed structural properties to computing aromatization energies. Where ever possible, the computed energies are compared to experimental data to demonstrate the high reliability of the chosen computational approach. The aromatic character of the cyclopropenyl cation and the triplet cyclopropynyl cation was demonstrated through their bond order uniformity, hydride ion affinities, frontier molecular orbital energy gaps, electron affinities, relative hydrogenation energies, and through newly computed aromatization energies. New thermodynamic values, such as the enthalpy of formation for all the three-carbon carbocations are computed with a computational error of ±2–3kcal/mol.