Effect of diffuse functions on the potential-energy surfaces of the alkylation reactions X^- + CH<inf>3</inf>F → XCH<inf>3</inf> + F^-(X = OH, CH<inf>3</inf>, H<inf>2</inf>CCHO)

The alkylation processes of the reactions X- + CH3F → XCH3 + F-, where X = OH, CH3 and H2CCHO, have been studied theoretically by means of 3-21 + G ab initio calculations. Transition states have been directly located. The use of a diffuse function-augmented basis set allows kinetically (O-alkylation) and thermodynamically (C-alkylation) controlled reactions of acetaldehyde enolate to be clearly separated. The changes of potential surfaces by the use of the 3-21 + G basis set instead of the 3-21G one are discussed, with special attention to the relevant modifications of transition structures. The influences of thermal corrections and electron correlation have also been considered.