Saturation and unsaturation effects on stability of divalent five membered ring: DFT calculations on carbenes, silylenes, germylenes, stanylenes and plumbylenes derivatives

Gibbs free energy differences between singlet and triplet states, ΔGt–s, are calculated for C4H4M, C4H6M and C4H8M (M = C, Si, Ge, Sn and Pb) at B3LYP/6-311++G (3df,2p) level. Singlet-triplet splitting, ΔGt–s, is compared for three analogues C4H4M, C4H6M and C4H8M. The change order of ΔGt–s is (except for M = C): C4H6M > C4H8M > C4H4M. The results of homodesmotic reaction energies show the most stability for singlet state of C4H6M respect to C4H4M and C4H8M. In contrast, the triplet state of C4H4M (except for M = C) is the most stable respect to C4H6M and C4H8M.