A High-Level ab Initio and Density Functional Investigation of Cyclopropenyl Anion and Its Mono-, Di-, and Trisubstituted Derivatives

High-level ab initio and density functional theory calculations were carried out on cyclopropenyl anion ( 1 ) and related species. The parent c-C 3 H 3 - ion is predicted to be unstable with respect to electron loss whereas its cyano-substituted derivatives are attractive synthetic targets. MCSCF structures for singlet and triplet cyclopropenyl anion are reported and contrasted to the results obtained from more modest computations. Energetic quantities for 1 were computed including its proton affinity, destabilization energy, singlet−triplet gap, electron binding energy, and ring-opening isomerization energy. The allylic C−H bond strength for cyclopropene also is given. Mono-, di-, and tricyanocyclopropenyl anions were investigated too, and their conjugate acids have lower p K a 's than cyclopropene by up to 70.4 kcal/mol or 52 p K a units.