A theoretical study on C–H bond dissociation enthalpies of oxygen-containing fused heterocyclic compounds

The C–H bond dissociation enthalpies (BDEs) of 27 N, O, S-containing mono-heterocyclic compounds were assessed by the composite high-level ab initio methods G4 and G3B3. After comparing the theoretical C–H BDEs of 32 N, O, S-containing heterocyclic compounds by using 10 density functional theory methods with experimental ones, we found that the BMK method provided the lowest root of mean square error of 7.2 kJ/mol. Subsequently, we calculated the C–H BDEs of oxygen-containing fused heterocyclic compounds at different positions by the BMK method. The results indicated that there are large BDE differences between the C( sp 3 )–H bonds. In order to find the essence of the C–H BDE differences, NBO and molecular orbital analyses were conducted. In addition, the substituent effects on C–H BDEs in oxygen-containing fused heterocyclic compounds were discussed. Finally, we found two linear relationships between the BDEs and qO/ e in the oxygen-containing fused heterocyclic compounds for different substituents, and the corresponding correlation coefficient squares ( R 2 ) were 0.8551 and 0.9379, respectively.