Stabilized carbenes do not dimerize

Dimerization Gibbs free energies were computed for several carbenes. At the B3LYP/6-311+G(2D) level the values are smaller than at MP2/6-311+G(2D) by about 10 kcal mol(-1), the DFT results being in accord with experimental fi ndings. The smallest dimerization energy was obtained for those compounds, which have already been synthesized (with proper substituent groups). The d imerization energy shows an excellent linear correlation with the stabiliza tion obtained in an isodesmic reaction, giving the possibility to estimate the stability of any new nucleophilic carbene by a simple computational pro cedure. In this estimate, however, only electronic factors are considered, steric effects (the use of bulky protecting groups) can give additional sta bilization.