Conformational Studies on Divalent Five-Membered Ring C4H4M (M = C, Si, Ge, Sn and Pb)

Abstract

Sum of electronic and thermal energy differences between   singlet and triplet states, ΔE_t-s; enthalpy differences, ΔH_t-s;   free energy differences, ΔG_t-s, are calculated for C₅H₄, C₄H₄Si,   C₄H₄Ge, C₄H₄Sn and C₄H₄Pb at B3LYP/6-311++G (3df,2p)   level of theory. Triplet state of carbene, C₅H₄, appears planar   and ground state while its corresponding singlet state is nonplanar.   In contrast, its analogues, C₄H₄M (M = Si, Ge, Sn and   Pb) in both singlet and triplet states have planar structures   with the ground state singlet. The order of energy differences   between singlet and triplet, ΔG_t-s, is: plumbylenes > stanylenes   > germylenes > silylenes > carbene.