The effects of substituent type and position on the aromaticity of certain derivatives of imidazole and benzimidazole

Nucleus-independent chemical shift (NICS) data were used to determine the aromaticity of the studied compounds. The influences of substituent type and position on the aromaticity of some derivatives of imidazole, 2- phenylimidazole, benzimidazole and 2-phenylbenzimidazole have been studied theoretically by DFT levels at B3LYP/6- 31+G* and B3LYP/6-311++G** methods. The studied compounds were optimized at the B3LYP/6-31+G* level. We have analyzed the aromaticities of these compounds with the substituents -CH3, -C2H5, -CH(CH3)2, -C(CH3)3, -OH, -OCH3, -NO2, -CN, -F, -Cl and -Br. The most efficient substitution to enhance the aromaticities was calculated to be at positions 5, 7 and ortho position for the studied compounds. The frontier molecular orbital energies (HOMO and LUMO) of the studied compounds were also calculated.