The C–H bond dissociation enthalpies in fused N-heterocyclic compounds

Abstract

The C–H bond dissociation enthalpies (BDEs) of the 26 N, O, S-containing mono-heterocyclic compounds were evaluated using the composite high-level ab initio methods G3 and G4. The C–H BDEs for 32 heterocyclic compounds were calculated using 8 types of density functional theory (DFT) methods. Comparing with the experimental values, the BMK method gave the lowest root mean square error (RMSE) of 7.2 kJ/mol. Therefore, the C–H BDEs of N-fused-heterocyclic compounds at different positions were investigated by the BMK method. By NBO analysis two linear relationships between the C–H BDEs of quinoline and isoquinoline with natural charges qC/e in molecules and with natural charges qC/e in radicals were found. The substituent effects on C_(α)–H BDEs in N-fused-heterocyclic compounds were also discussed. It was found that there are two linear relationships between the C_(α)–H BDEs of quinoline and isoquinoline derivatives with natural charges qC_(α)/e for the EDGs and CEGs substituents.