Heteroatom Effects on Singlet–Triplet Energy Gaps of Divalent Five-Membered Ring X₂C₂H₂C (X = N, P, As, and Sb)

Abstract

Thermal energy gaps, ΔE_s–t; enthalpy gaps, ΔH_s–t; and Gibbs free energy gaps, ΔG_s–t between the singlet (s) and triplet (t) states of X₂C₂H₂C, 1_X (X = CH, N, P, As, and Sb) were calculated and compared with those analogues, XC₂H₃C, 1′_X (X = N, P, As, and Sb) at the B3LYP/6-311++G** level of theory. Density functional theory (DFT) calculations indicated that the ΔG_s-t, for 1_X (X = N and P) should be lower with respect to their monosubstituted 1′_X . In contrast, the ΔG_s-t for 1_X (X = As and Sb) should be larger with respect to 1′_X . The ΔG_s-t for 1_X and 1′_X were increased in the following order: 1_Sb > 1_As > 1_C > 1_P > 1_N ; 1′_Sb > 1′_As > 1′_P > 1_C > 1′_N , respectively.

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Keywords:

• Carbene
• five-membered ring
• heteroatom
• singlet–triplet energy gap; X₂C₂H₂C