Experimental investigations of proton transfer reactions and transacylation reactions in the gas phas

Two classes of gas phase ion-molecule reactions were studied using ion cyclotron resonance (ICR) spectrometry: proton transfer and transacylation.;The kinetics of proton transfer reactions between alkoxide ions and neutral alcohols were monitored. Reaction efficiencies for thermoneutral proton transfers were found to be slower than the collision efficiency, suggesting a substantial barrier on the reaction potential surface. The efficiency trend for exothermic reactions was also found to be consistent with a barrier. These slow rates are not consistent with expectations based on solution behavior or with ab initio calculations suggesting a surface with a negligible barrier.;The solvated alkoxide ions assumed to be proton transfer reaction intermediates were synthesized in the ICR spectrometer. Isotope labeling was used to differentiate between the two possible complexes: ROH$cdotsp{-}$OR$spprime$, and R$spprime$OH$cdotsp{-}$OR. The structure of the two isomers was probed using infrared multiple photon dissociation; the ratio of ionic photoproducts was found to depend on the isomer. This indicates the two complexes are distinct, suggesting a bottleneck on the proton transfer potential surface, consistent with the kinetic observations. The difficulty in reconciling these results with the quantum calculations remains.;Investigations of transacylation reactions are described. A deprotonated hemiacetal ion was used as a model transacylation reaction intermediate. The acidity of the cyclic hemiacetal, 2-hydroxytetrahydropyran, was found to be quite strong: $Delta$G$sbsp{rm acid}{rm o}$ = 352 $pm$ 2 kcal/mol, implying tetrahedral reaction intermediates are quite stable. Thermochemical arguments are presented suggesting that tetrahedral adducts of this type are often global minima on the reaction potential surface.;The transacylation reactions of solvated alkoxide ions with a series of alkyl formates and esters were studied. Reaction of alkoxide$cdot$alcohol complexes with alkyl formates resulted in transesterification and efficient transfer of the alcohol "solvent" molecule from the reactant to the product ion. The reaction of the alkoxide$cdot$alcohol complexes with esters CF$sb3$COOMe and PhCOOMe, resulted in direct formation of the ionic transacylation reaction intermediate. The chemical and photochemical behavior of the (CF$sb3$COOMe + MeO$sp{-}$) adduct was investigated; its properties are most consistent with being a stable, covalently bound tetrahedral species. A generalized scheme for gas phase transacylation reactions is presented.