α-Sulfonyl Carbanions:  Combined Kinetic, Thermodynamic, and NMR Approaches for the Study of the Ionization of Benzyltriflones in Me2SO and H2O−Me2SO Mixtures

• Published in: Journal of the American Chemical Society Vol. 120; no. 37; pp. 9496 - 9503
• Main Authors: Terrier, F, Kizilian, E, Goumont, R, Faucher, N, Wakselman, C
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23-09-1998
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja9806074

The ionization of a series of benzyltriflones ArCH2SO2CF3 (Ar = C6H5, 4-CNC6H4, 4-NO2C6H4, 2,4-(NO2)2C6H3, 2,4,6-(NO2)3C6H2) has been studied kinetically and thermodynamically as well as by 1H, 13C, and 19F NMR in H2O−Me2SO mixtures and/or Me2SO. The findings that the acidity of the triflones is enhanced on going from hydroxylic solvents to Me2SO and that their deprotonation is associated with high Marcus intrinsic reactivities are two major results indicating the presence of a large polarizable charge density at Cα of the carbanionic species. Comparison of the results obtained with those for related arylnitromethane and arylacetonitrile compounds strongly supports this conclusion. NMR data add to the evidence that polarization rather than d−p π-resonance or negative hyperconjugation is the dominant factor in accounting for the capability of the strongly electron withdrawing SO2CF3 group to stabilize negative charge. Altogether, our results lead to a structural picture of the triflone carbanions in solution which does not totally fit the conclusions reached on the basis of solid-state or computed gas-phase studies.