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

Abstract Full geometry optimizations were carried out on singlet and triplet states of α-substitued divalent five-membered rings XC 4 H 3 M (X = –NH 2 , –OH, –CH 3 –H, –CH 3 , –Br, –Cl, –F, –CF 3 and –NO 2 ; M = C, Si and Ge) by B3LYP method using 6-311++G** basis set. Thermal energy gaps, Δ E s–t ; enthalpy gaps, Δ H s–t ; Gibbs free energy gaps, Δ G s–t , between singlet (s) and triplet (t) states of above structures were calculated using the GAUSSIAN 03 program. The Δ G s–t of XC 4 H 3 C was changed in the order: X = –Cl > –Br > –CH 3  > –H > –CF 3  > –F > –NO 2  > –OH > –NH 2 . The changes of Δ G s–t for XC 4 H 3 Si and XC 4 H 3 Ge were in the order: X = –NH 2  > OH > F > Cl > Br > CH 3  > H > CF 3  > NO 2 . 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, Δ N max , was presented and discussed.