Steric effects on the Singlet–Triplet Energy Gaps of Seven Membered Ring silylenes, R2C6H6Si

With the aim of recognizing the steric effects on the silylenic R2C6H6Si structures, DFT calculationsare carried out on 8 structures of R2C6H6Si (where R is hydrogen (H), methyl (Me), isopropyl (i-pro),and tert-butyl (tert-Bu)). These species are at either triplet (t) or singlet (s) states. Singlet–tripletenergy separations (<Gt-s) and relative energies for the above structures are acquired at B3LYP/6-31G** levels of theory. The <Gt–s of R2C6H6Si was increased in the order (in kcal/mol): H (23.73) >i-Pr (20.56) > Me (20.32) > t-Bu (15.92).all singlet states of R2C6H6Si, are more stable than theircorresponding triplet states. linear correlations are encountered between the LUMO–HOMO energygaps of the singlet(stable) states of R2C6H6Si compounds, and their corresponding singlet–tripletenergy separations are calculated at B3LYP/6-311++G∗∗ level of theory. Other geometricalparameters such as bond angles, dihedral angles, bond lengths, NBO charge at atoms, dipolemoments (D), (HOMO), (LUMO), chemical hardness (F), chemical potential (G), electrophilicity (H)and the maximum amount of electronic charge, <Nmax were calculated and discussed.