Substitution effects at α-position of divalent five-membered ring XC4H3M (M = C, Si and Ge)

Full geometry optimizations were carried out on singlet and triplet states of α-substitued divalent five-membered rings XC4H3M (X = –NH2, –OH, –CH3 –H, –CH3, –Br, –Cl, –F, –CF3 and –NO2; M = C, Si and Ge) by B3LYP method using 6-311++G** basis set. Thermal energy gaps, ΔEs–t; enthalpy gaps, ΔHs–t; Gibbs free energy gaps, ΔGs–t, between singlet (s) and triplet (t) states of above structures were calculated using the GAUSSIAN 03 program. The ΔGs–t of XC4H3C was changed in the order: X = –Cl > –Br > –CH3 > –H > –CF3 > –F > –NO2 > –OH > –NH2. The changes of ΔGs–t for XC4H3Si and XC4H3Ge were in the order: X = –NH2 > OH > F > Cl > Br > CH3 > H > CF3 > NO2. The relationship between all the parameters such as different energy types, geometry parameters, natural bonding orbital (NBO) charge at atoms, HOMO and LUMO energies, chemical hardness (η), chemical potential (μ), dipole Moment (D), electrophilicity (ω) and the maximum amount of electronic charge, ΔNmax, was presented and discussed.