Trends in alkyl substituent effects on nucleophilic reactions of carbonyl compounds: Gas phase reactions between ammonia and R1R2COCH3+ oxonium ions

Abstract

The reactivity of carbonyl substituted methyl oxonium ions (R¹R²COCH₃⁺) towards ammonia has been investigated using an FT-ICR mass spectrometer and ab initio calculations. The monosubstituted ions (R¹=H; R²= H, CH₃, C₂H₅ and i-C₃H₇) show different reaction patterns with variable degree of: (1) nucleophilic substitution, (2) addition–elimination and (3) proton transfer, when reacted with ammonia. In all cases addition–elimination dominates over nucleophilic substitution, and the observed reactions are slow. The trends in reactivity are consistent with the alkyl group's electronic properties, as expressed by a single parameter linear or slightly non-linear model.