A study of energetics of formation of heterocomplexed cations of trimethylamine N-oxide by using ab initio methods

Abstract

Ab initio methods at the Restricted Hartree Fock (RHF) and Møller–Plesset (MP2) levels were used to investigate the energetics of heterocomplexed cation formation by trimethylamine N-oxide as the proton donor and substituted pyridine N-oxides of different basicities. For calculation of the energies and Gibbs free energies of cationic heteroconjugation, a 6–31G ∗ basis set was used in which, the polarization function was accounted for. The calculated energies, Δ E BHB 1 + , and Gibbs free energies, Δ G BHB 1 + , of formation of the heterocomplexes in vacuo have been found to correlate well with the corresponding calculated energies and Gibbs free energies of protonation of the proton acceptor (at fixed proton donor basicity) and slightly less so with experimental cationic heteroconjugation constants, log K BHB 1 + , determined in nitromethane.