Extraordinary β-silyl effects on C-H, N-H, and O-H bond dissociation energies

Composite ab initio G3 calculations show that most of the β substituents have very little effects (less than 2 kcal/mol) on the C-H, N-H, and O-H bond dissociation energies (BDEs). However, β-silyl groups are found to be able to dramatically reduce the C-H, N-H, and O-H BDEs by ca. 3, 6, and 10 kcal/mol, respectively. Natural bond orbital analysis suggests that the extraordinary β-silyl effect is caused by the strong hyperconjugation interaction between the σSi-C bonding orbital and the half-filled p-orbital of the radical center.