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 a cids and methoxide ion in methanol. This is refined for several compou nds 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 report ed to evaluate the stability of possible intermediates along the react ion pathway from 2-hydro-2-phenyl-perfluoropropane and methoxide ion t o the carbanion and methanol. The intermediate, {C6H5C(CF3)(2)}(-).. H OCH3, is 6.8 kcal/mol more stable than the separated species, {C6H5C(C F3)(2)}(-) and CH3OH, and 43.2 kcal/mol more stable than C6H5CH(CF3)(2 ) and -OCH3.