The role of substituent on the aromaticity variation of mono- and di-substituted aza analogs of indole

Electronically-based indices (ATI and FLU) have been employed to investigate the substituent effect on the π-electron delocalization in both heterocyclic and benzenoid rings of mono- and di-substituted aza analogous of indole. Three typical substituents (Cl, OCH3 and CN) with different inductive and resonance effects have been selected. Generally, substituent causes a reduction in aromaticity irrespective of whether it is electron-attracting or electron-donating. It is shown that maximum aromaticity exhibits a similar trend of Cl > CN > OCH3 for all studied rings. Moreover, it is found that the substituent situation with respect to heteroatom has a significant influence on the aromaticity. In di-substituted derivatives, irrespective of their positions relative to each other, they preferably choose the position that leads to maximum aromaticity character.