β-Position Electronic Effects on the Singlet–Triplet Gaps of Divalent Five-Membered Rings XC4H3M (M˭C, Si, and Ge)

Abstract Full geometry optimizations were carried out on the singlet and triplet states of β-substituted divalent five-membered rings XC4H3M (X˭ ‒NH2, ‒OH, ‒CH3 ‒H, ‒CH3, ‒Br, ‒Cl, ‒F, ‒CF3, and ‒NO2; M˭C, Si, and Ge) by the B3LYP method by using 6-311++G** basis set. The thermal energy gaps, ΔEt–s; enthalpy gaps, ΔHt–s; and Gibbs free energy gaps, ΔGt–s, between the singlet (s) and triplet (t) states of the above structures were calculated by using the GAUSSIAN 03 program. The ΔGt–s of XC4H3C was changed in the order: X˭ ‒Cl > ‒Br > ‒CH3 > ‒H > ‒CF3 > ‒F > ‒NO2 > ‒OH > ‒NH2. The changes of ΔGt–s for XC4H3Si and XC4H3Ge were in the order: X˭ ‒NH2 > OH > F > Cl > Br > CH3 > H > CF3 > NO2. The geometrical parameters, including bond lengths (R), bond angles (A), dihedral angles (D), natural bonding orbital (NBO) charge at atoms, HOMO and LUMO, and dipole moments, were presented and discussed. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, an...