ALPHA-SULFONYL CARBANIONS - COMBINED KINETIC, THERMODYNAMIC, AND NMR APPROACHES FOR THE STUDY OF THE IONIZATION OF BENZYLTRIFLONES IN ME2SOAND H2O-ME2SO MIXTURES

The ionization of a series of benzyltriflones ArCH2SO2CF3 (Ar = C6H5, 4-CNC6F4, 4-NO2C6H4, 2,4-(NO2)(2)C6H3, 2,4,6-(NO2)(3)C6H2) has been st udied kinetically and thermodynamically as well as by H-1, C-13, and F -19 NMR in H2O-Me2SO mixtures and/or Me2SO. The findings that the acid ity of the triflones is enhanced on going from hydroxylic solvents to Me2SO and that their deprotonation is associated with high Marcus intr insic reactivities are two major results indicating the presence of a large polarizable charge density at C-alpha of the carbanionic species . Comparison of the results obtained with those for related arylnitrom ethane and arylacetonitrile compounds strongly supports this conclusio n. NMR data add to the evidence that polarization rather than d-p pi-r esonance or negative hyperconjugation is the dominant factor in accoun ting for the capability of the strongly electron withdrawing SO2CF3 gr oup to stabilize negative charge. Altogether, our results lead to a st ructural picture of the triflone carbanions in solution which does not totally fit the conclusions reached on the basis of solid-state or co mputed gas-phase studies.