A DFT study of endocyclic allenes: unprecedentedly superbasic hydrocarbons

Abstract

Density functional theory (DFT) calculations using the B3LYP, M05-2X and M06-2X functionals were employed in the study of basicity of allenes incorporated in seven-membered rings. These highly unstable species upon protonation give thermodynamically very stable tropylium cations, which are the origin of their extremely high basicity. An endocyclic allene → tropylium cation sequence was used for the design of novel hydrocarbon superbases, with calculated gas phase proton affinities exceeding well above 300 kcal mol⁻¹.