Easy and accurate computation of energy barriers for carbocation solvation: an expeditious tool to face carbocation...

An expeditious procedure for the challenging computation of the free energy barriers (ΔG^≠) for the solvation of carbocations is presented. This procedure is based on Marcus Theory (MT) and the popular B3LYP/6-31G(d)//PCM method, and it allows the easy, accurate and inexpensive prediction of these barriers for carbocations of very different stability. This method was validated by the fair mean absolute error (ca. 1.5 kcal mol^-1) achieved in the prediction of 19 known experimental barriers covering a range of ca. 50 kcal mol^-1. Interestingly, the new procedure also uses an original method for the calculation of the required inner reorganization energy (Λ_i) and free energy of reaction (ΔG). This procedure should pave the way to face computationally the pivotal issue of carbocation chemistry and could be easily extended to any bimolecular organic reaction.