Acetamide enolate: Formation, reactivity, and proton affinity

Acetamide enolate (1) was selectively prepared in a Fourier transform mass spectrometer and a variable temperature flowing afterglow apparatus by the fluoride-induced desilylation of 2-(trimethylsilyl)acetamide. Its reactivity, proton affinity, and collision-induced dissociation spectra were explored and contrasted to its isomeric amidate anion (2). Since 1 and 2 are ambident nucleophiles, their reactivity with perfluoropropylene and perfluorobenzene was investigated. The unimolecular isomerization of 1 to 2 also was examined at temperatures up to 300°C. No rearrangement was observed under these conditions indicating that the activation barrier is at least 32 kcal mol^-1. Structures and energies of acetamide, its conjugate bases, and the transition structure interconverting 1 and 2 were computed using a variety of ab initio and density functional theory approaches.