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.