Ab Initio Study of the Solvent Effects on the Singlet−Triplet Gap of Nitrenium Ions and Carbenes

Abstract

Highly correlated ab initio molecular orbital methodologies have been used in the study of substituent effects on the singlet−triplet gaps of a series of nitrenium ions and their corresponding isoelectronic carbenes. Calculations in solution were carried out with the isodensity polarizable continuum models, IPCM. The results show a net stabilization of the singlet species as a result of electronic density donation of the substituents to a vacant p orbital located in the central atom. It is shown that this “π-donor−π-acceptor” dependence of the singlet−triplet gap is more significant in the case of the nitrenium ions, due to the presence of a positive charge. In addition, it was found that the singlet−triplet gaps decrease with the polarity of the solvent, most likely due to stabilizing electrostatic interactions between the solvent and the charge distribution of the singlet.