Theoretical Study of the C-Cl Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds

Quantum chemical calculations were used to estimate the bond dissociation energies (BDEs) for 13 substituted chlorobenzene compounds. These compounds were studied by the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 6-31G**and 6-311G** basis sets. The results show that B3P86/6-311G** method is the best method to compute the reliable BDEs for substituted chlorobenzene compounds which contain the C-Cl bond. It is found that the C-Cl BDE depends strongly on the computational method and the basis sets used. Substituent effect on the C-Cl BDE of substituted chlorobenzene compounds is further discussed. It is noted that the effects of substitution on the C-Cl BDE of substituted chlorobenzene compounds are very insignificant. The energy gaps between the HOMO and LUMO of studied compounds are also investigated and from this data we estimate the relative thermal stability ordering of substituted chlorobenzene compounds.