SUBSTITUENT EFFECT ON THE DISSOCIATION-ENERGY OF THE SI-H BOND - A DENSITY-FUNCTIONAL STUDY

The bond dissociation energies of a series of substituted silanes have been studied with quantum mechanics density functional calculations. Successive Me, F substitutions strengthen the Si-H bond, while MeO, Cl, Pr, SMe, SiH3, as well as Ph groups weaken the bond. These mostly agree with experimental measurements and previous ab initio calculations. The calculated substituent effect can be correlated reasonably well with the calculated Hirshfeld charge and spin density variations on the Si radical center. While radical spin delocalization reduces the bond strength, withdrawing inductive character of the substituents increases the Si-H bond strength. The second-row element substituents have larger radical spin delocalization ability, which is responsible for the greater reduction of the Si-H bond dissociation energy