Aromatization Energy of Cyclopropenyl Cation

Abstract

A radical based homodesmotic reaction (HDR) is designed for the accurate calculation of the aromatic stabilization energy of cyclopropenyl cation. The energy of the HDR (ΔE) accounts for the energy released when the cyclic 2π electron cationic conjugation is changed to a linear 2π electron cationic conjugation. In other words, ΔE corresponds to the aromatic stabilization energy of cyclopropenyl cation. The value of the aromatic stabilization at G2 level is found to be 127.0 kJ/mol. This stabilization energy is much smaller as compared to the value of 247.3 kJ/mol calculated by Glukhovtsev et al. in 1996 using a reaction falsely described as a homodesmotic reaction. In fact, their value accounted mainly the total π electron conjugation energy of (C₃H₃)⁺ and not to its aromatic stabilization. B3LYP/6-31G(d,p) and G2 level calculations on homodesmotic reaction were used in this study. The aromatic stabilization energy of cyclopropenyl cation at B3LYP/6-31G(d,p) and G2 levels are, respectively, 115.4 and 127.0 kJ/mol. A new homodesmotic reaction is designed for the accurate estimation of the aromatic stabilization energy of cyclopropenyl cation.