Characterization of an ambident electrophile: the gas phase reactivity of the methoxymethyl cation

The gas phase reactivity of the methoxymethyl cation, an ambident electrophile, towards 21 neutral nucleophiles has been probed using the flowing afterglow technique. The classes of compounds studied includes alcohol, ethers, thiols, thioethers, aliphatic ketones, acids, eaters and amides as well as the following aromatics: benzene, pyridine and aniline. Three general types of reaction channels were observed: addition followed by elimination of methanol with concomitant [M + CH](+) ion formation S(N)2 methylation resulting in [M + CH3](+) ion formation and adduct ([M + CH3OCH2](+)) formation. Formamide and N,N-dimethylformamide both yield additional products arising from cleavage of the amide bond by CH3OCH2+. In addition, ab initio techniques (at the MP2(fc)/6-31G* level) have been used to investigate the [M + CH](+) and [M + CH3](+) ion formation channels for the reactions of CH3OCH2+ with NH3, H2O and H2S. These ab initio results suggest that the reactivity order should be: NH3 > H2S > H2O, in line with the experimental observations. (C) 1998 Elsevier Science B.V. All rights reserved.