Abstract

The para13C shifts of benzylcarbanions PhCH–X (VI) in Me2SO, acidities of toluene carbon acids PhCH2X (I) in Me2SO, and gas-phase acidities of methane carbon acids CH3X (VIII) are submitted to mono- and bi-parametric substituent treatment using previously defined sets of σc–, σIB, and σR– constants. It is confirmed that these scales are appropriate for describing interactions between contiguous functionalities, as opposed to literature values which account for remote interactions. Gas-phase acidities respond excellently to substituent effect treatment, while solution data show deviations for the SO2R and CN substituents. Such deviances are accounted for as a manifestation of SSSAR (Stabilization due to Specific Solvent Assisted Resonance) for groups which exhibit extensive charge transfer from the carbanionic carbon to the π-accepting substituent (COR, CO2R, CONMe2, NO2, etc.). The mesomeric component of substituent effects is about three times more important than the polar–inductive one in governing the acidities of carbon acids in Me2SO solution and in affecting the chemical shift of the para monitor in PhCH–X. Relative to the gas phase, the solvent enhances by a factor of 2 the sensitivity of acidities of carbon acids to the mesomeric components of substituent effects. The sensitivity of the para monitor in PhCH–X to polar–inductive components of substituent effects shows, relative to the neutral precursor PhCH2X (I), a three-fold increase and, relative to the PhNHX family, a two-fold increase. The sensitivity of the para monitor in PhCH–X to mesomeric components of substituent effects shows a three-fold increase relative to the PhNHX family.

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