DFT investigation of the thermodynamics and mechanism of electrophilic chlorination and iodination of arenes

Quantum chemical calculations at the B3LYP/6-311G* level have been carried out in order to investigate the reaction mechanisms of the iodination of benzene and its monosubstituted derivatives with ICl, I+, I3+ and reagents containing N–I and O–I bonds as the iodinating agents. The results are compared with those obtained for chlorination by Cl+ and Cl2, both in the gas phase and in methanol solution using the PCM solvent model. We have also used the MP2/DGDZVP level of theory and the IEFPCM model to perform comparisons in a few cases. The thermodynamic parameters for the reactions have been calculated, the structures of the intermediate products (π- and σ-complexes) and transition states have been optimized, and the profiles of the free energy surfaces have been constructed.