Acidity inversions of alpha-NO2 and alpha-SO2CF3 activated carbon acids as a result of contrasting solvent effects on transfer from water to dimethyl sulfoxide solutions.
Measurements of pK(a) values for the ionization of alpha-X-substituted ethyl acetates (1, X = NO(2); 2, X = CN; 3, X = SO(2)CF(3)) in H(2)O[bond]Me(2)SO mixtures and pure Me(2)SO show a unique response of the acidity of the SO(2)CF(3) derivative to the solvent changes, thereby resulting in a remarkable inversion in the acidifying effects of the strongly electron-withdrawing NO(2) and SO(2)CF(3) groups on going from H(2)O to Me(2)SO. Overall, the results obtained provide strong evidence that the powerful electron-withdrawing effect of the SO(2)CF(3) group is by far the result of polarization effects rather than other factors such as negative hyperconjugation.
Goumont
Régis
R
Laboratoire SIRCOB, UMR 8086, Institut Lavoisier-Franklin, Université de Versailles, 45, Avenue des Etats-Unis, 78035 Versailles Cedex, France.
Magnier
Emmanuel
E
Kizilian
Elyane
E
Terrier
François
F