β-Cyanoethyl Anion: Lusus Naturae

A stable E1cb intermediate, β-cyanoethyl anion
(1β), has been synthesized in the gas phase at
room
temperature under thermal conditions via the fluoride-induced
desilylation of 3-(trimethylsilyl)propionitrile.
The
reactivity and thermodynamic properties of this ion are reported.
The cyano group is found to lower the proton
affinity of 1β by 29 ± 6 kcal/mol, which represents a
particularly large substituent effect. High-level ab initio
and
density functional calculations have been carried out on
1β and several related species. The computational
results
are compared to each other, and their accuracy is
evaluated.