Figure illustrates the principle for pyrazole and N-methylimidazole. For pyrazole the predictions point exclusively to the 4-position; indeed literature examples of the other regioisomer being formed were not identified. The situation is more complex for N-methylimidazole with both 4 and 5 positions as potential sites for the reaction. This correlates well with the moderate yield of 42%. Indeed the 4,5-dihalogenated adduct can be obtained in synthetically useful yields. In fact all three positions in N-methylimidazole can be halogenated which is not surprising given the fact the calculations suggest that the three possible arenium ions have similar standard free energies. Finally, a 1:1 mixture of the 4-and 5-brominated products has been reported for N-benzylimidazole, which is in line with the predictions.