Monte Carlo simulations and MO calculations were carried out for three carbon-centered radicals, CH(OH)CN, CH(OH) 2 and CH(CN) 2, in H 2O, and the relative stability of these radicals was examined in connection with the substitution pattern. The solvation free energy changes along the OH rotation were calculated for CH(OH)CN and CH(OH) 2 by statistical perturbation theory, and the energy minimum conformations of these radicals were determined. The solvation free energy differences among the three radicals were calculated by the mutation technique, and merostabilization energy of CH(OH)CN in water was calculated to be −17.52 kcal mol −1, which is much larger than that in the gas phase. The electronic structures of these radicals in the H 2O solution were calculated by ab initio ROHF MIDI-4 ∗ MO method including the solvent H 2O molecules represented by point charge approximation. The calculated charge and spin populations indicated that the large stabilization energy of CH(OH)CN in H 2O was caused by a strong interaction between the OH group of CH(OH)CN and H 2O, and this effect was found only in CH(OH)CN which is substituted asymmetrically by electron-donor and electron-acceptor groups.