Flowing afterglow study of the gas phase nucleophilic reactions of some formyl, acetyl and cyclic esters

A variety of nucleophiles have been investigated for their reactions with f ormyl and acetyl esters in the gas phase in our flowing afterglow. The reac tions that are permitted in the gas phase are more varied than those seen i n the condensed phase. The rates of reactions of methyl and ethyl esters as well as various lactones have been undertaken with various nucleophiles: H 2N-, HO-, CH3O-, NCCH2-, F-, CH3C(=O)CH2- CH3S- and O2NCH2-. For example, t he reaction rate of NCCH2- + HCO2CH2CH3 has been found to be (1.3 +/- 0.2) x 10(-10) cm(3) molecule(-1) s(-1) and the only product is HC(O-)=CHCN whic h results from nucleophilic acyl substitution (B(AC)2) followed by a proton transfer within the ion-molecule complex. Other reaction mechanisms that h ave been observed include beta-elimination (E2), bimolecular nucleophilic s ubstitution at the alkyl group (B(AL)2), and the Riveros reaction (eliminat ion of CO). A mechanism for the F- + HCO,CH, reaction has been determined a t the B3LYP/6-31 + G(d) level. Most notably, channels were determined compu tationally (B(AL)2 and Riveros), and these channels are also observed exper imentally. Furthermore, the B(AC)2 pathway which proceeds via nucleophilic attack on the carbonyl group also leads to the Riveros products, F-(CH3OH) and CO.