Proton transfer between carbon acids and methoxide: Studies in methanol, the gas phase and by ab initio MO calculations

A detailed mechanism that features hydrogen-bonded carbanions as well as free carbanions is presented for hydrogen transfer between carbon acids and methoxide ion in methanol. This is refined for several compounds by measuring their gas phase acidities, Delta G(Acid)(0) kcal/mol: C6H5CH(CF3)(2) [335.3]; p-C6H4CHClCF3 [337.4]; 9-phenylfluorene [335.6]; C6F5H [349.2]. Ab initio molecular orbital calculations are reported to evaluate the stability of possible intermediates along the reaction pathway from 2-hydro-2-phenyl-perfluoropropane and methoxide ion to the carbanion and methanol. The intermediate, {C6H5C(CF3)(2)}(-).. HOCH3, is 6.8 kcal/mol more stable than the separated species, {C6H5C(CF3)(2)}(-) and CH3OH, and 43.2 kcal/mol more stable than C6H5CH(CF3)(2) and -OCH3.