TY - JOUR
T1 - The α-effect and competing mechanisms
T2 - the gas-phase reactions of microsolvated anions with methyl formate
AU - Thomsen, Ditte Linde
AU - Nichols, Charles M.
AU - Reece, Jennifer N.
AU - Hammerum, Steen
AU - Bierbaum, Veronica M.
PY - 2014/2
Y1 - 2014/2
N2 - The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase SN2 reactions of the microsolvated HOO-(H2O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO-(H2O) with that of microsolvated normal alkoxy nucleophiles, RO-(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO-(H2O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated α-nucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the SN2 and BAC2 reactivity compared with the unsolvated analogs. HOO-(H2O) reacts with methyl formate exclusively via the BAC2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the B AC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction. [Figure not available: see fulltext.]
AB - The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase SN2 reactions of the microsolvated HOO-(H2O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO-(H2O) with that of microsolvated normal alkoxy nucleophiles, RO-(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO-(H2O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated α-nucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the SN2 and BAC2 reactivity compared with the unsolvated analogs. HOO-(H2O) reacts with methyl formate exclusively via the BAC2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the B AC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction. [Figure not available: see fulltext.]
U2 - 10.1007/s13361-013-0781-z
DO - 10.1007/s13361-013-0781-z
M3 - Journal article
C2 - 24346962
SN - 1044-0305
VL - 25
SP - 159
EP - 168
JO - Journal of The American Society for Mass Spectrometry
JF - Journal of The American Society for Mass Spectrometry
IS - 2
ER -