Mechanisms of bromination between thiophenes and NBS: A DFT investigation

Abstract

Mechanisms for bromination between thiophenes and NBS have been investigated at level of M06-2X-D3/ma-def2-TZVP, and SMD model was taken to simulate the solvent effect of chloroform. The computational results of Gibbs free energy surfaces point out that the paths of forming bromonium ion are favorable. So, Br2 and NBS could provide the source of Br to achieve the bromination process to obtain the final product 2,5-dibromothiophenes. Br2 is trace amount in the reagent of NBS, we speculate that the path with the participation of NBS could happen in large amounts in the reactive system and the path with participation of Br2 could also be occurred in smaller amount. Meanwhile, the relations between the order of forming bromonium ion and energy barriers have been discussed. Fukui function can be used to predict the reactive sites, and frontier orbital theory can analyze the HOMO and LUMO of reactants.