Substituent effects on stability, MEP, NBO analysis, and reactivity of 2,2,9,9-tetrahalosilacyclonona-3,5,7-trienylidenes, at density functional theory

Cyclonona-3,5,7-trienylidene appears as boat-shaped transition state for having a negative force constant, while its singlet state exhibits less stability than the corresponding triplet state. Succeeding the quest for the largest unsaturated stable carbene-like species, theoretical investigations coupled with suitable isodesmic reactions are used to examine the effects of α , αʹ -tetrahalo groups on the thermodynamic along with kinetic viabilities of nine-membered cyclic silylenes. All the singlet and triplet silylenes appear as boat-shaped minima for having positive force constants on their potential energy surfaces and singlet states emerge as ground state, exhibiting more stability than their corresponding triplet states. The order of stability estimated by singlet (S)–triplet (T) energy separation (Δ E S–T = E T − E S ) emerges as α , αʹ -tetrahydrocarbene