Abstract
Since many organic reactions proceed in solvent, it is important to determine theoretical σ+ values for solution phase. For this purpose, it is necessary to know appropriate solvation models which reproduce the stabilities for the standard system of α-cumyl cations in solution. In this point of view, stabilities of α-cumyl cation coordinated by water molecule(s) (n=1-6) at cationic center were determined by means of hydride transfer reactions between ring substituted and unsubstituted cations. Energies for all species were calculated at the MP2/6-31G*//RHF/6-31G* level using Gaussian 98 program. The Yukawa-Tsuno analyses for the stabilities of hydrated α-cumyl cation with theoretically determined gas phase sigma values gave excellent linear correlations. While the r value didn't change so much, the absolute rho value decreased significantly with the number (n) of the water molecule down to 50% for the n = 6 system. When the substituent effect for this system was correlated with Brown and Okamoto's σ+ which is determined in solvolysis, deviations from the correlation line were observed for m-MeO and p-OH, indicating that specific solvation to the particular substituents is also important as a factor of appropriate solvation model.
