Comparison of alkyl substitution effects on singlet-triplet splitting of silylene with carbene

Full geometry optimizations have been carried out on singlet and triplet states of alkyl substituted acyclic silylene by B3LYP method using 6-311++G** basis set of the Gaussian 98 system of program. In contrast to carbene CH2, the singlet state of silylene (SiH2) is ground state. Similar to carbene, stability of singlet state is increased with substituting of alkyl groups on silylenic center. By comparing NBO charges on silylenic center of SiH2 and other large substituted acyclic silylenes, the role of methyl group is electron withdrawing respect to hydrogen atom. Higher electronegativity of methyl group leads to stabilize the singlet respect to triplet state as well as decreasing the singlet-triplet splitting energies.