A comparison of the C-H bond dissociation enthalpies of sulfur-containing fused heterocyclic compounds to the C-H bond dissociation enthalpies in other heterocycles

The C-H bond dissociation enthalpies (BDEs) of 26 N, O, S-containing mono-heterocyclic compounds were assessed by the composite high-level ab initio methods G4 and CBS-QB3. In addition, the C-H BDEs of 32 heterocyclic compounds were evaluated by 13 density functional theory methods. The BMK method showed the lowest root mean square error of 7.2 kJ/mol and the correlation coefficient (R-2) was 0.9874 after being compared with the experimental values. Subsequently, we used this method to study the C-H BDE values of the different positions as well as the substituent effects on benzene and heterocycles in sulfur-containing fused heterocyclic compounds. Both the natural charge distributions of benzo[b]thiophene and benzothiazole and natural spin densities of benzo[b]thiophene derivative radicals were conducted by NBO analysis for further understanding the essence of the C-H bond.