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 formyl and acetyl esters in the gas phase in our flowing afterglow. The reactions that are permitted in the gas phase are more varied than those seen in the condensed phase. The rates of reactions of methyl and ethyl esters as well as various lactones have been undertaken with various nucleophiles: H2N–, HO–, CH3O–, NCCH2–, F–, CH3C(O)CH2–, CH3S– and O2NCH2– . For example, the reaction rate of NCCH2– + HCO2CH2CH3 has been found to be (1.3 ± 0.2) × 10–10 cm3 molecule–1 s–1 and the only product is HC(O–)CHCN which results from nucleophilic acyl substitution (BAC2) followed by a proton transfer within the ion–molecule complex. Other reaction mechanisms that have been observed include β-elimination (E2), bimolecular nucleophilic substitution at the alkyl group (BAL2), and the Riveros reaction (elimination of CO). A mechanism for the F– + HCO2CH3 reaction has been determined at the B3LYP/6-31+G(d) level. Most notably, channels were determined computationally (BAL2 and Riveros), and these channels are also observed experimentally. Furthermore, the BAC2 pathway which proceeds via nucleophilic attack on the carbonyl group also leads to the Riveros products, F–(CH3OH) and CO.