Trends in R−X Bond Dissociation Energies (R• = Me, Et, i-Pr, t-Bu, X• = H, Me, Cl, OH)

Trends for R-X bond dissociation energies have been examined with density functional methods of B3LYP, BMK, M06-2X, MC3MPW, B2PLYP, MCG3-MPW, and XYG3, as well as G3, MCG3/3, G3X, and G4 theories as functions of alkylation (i.e., R(•) = Me, Et, i-Pr, t-Bu) and X(•) substitution (i.e., X(•) = H, Me, Cl, OH). The results highlight the physical origin of success or failure of each method and demonstrate the good agreement with experimental results for G4, MCG3-MPW, and XYG3. The last holds great promise as a reliable method that is applicable to larger systems.