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Continuing in our researches on the syntheses, reactivity, pharmacological/biological activities of heterocyclic compounds containing one or more nitrogen atoms we have examined some chemico-physical properties (1H and 13C NMR, electrochemical behavior, and ESR) of three series of 2-aryl-5(or 6)-nitrobenzimidazoles (1-3) variously substituted in the 2-aryl ring. The electrochemical behavior of the nitro group on the benzimidazole ring has been studied by cyclic voltammetry. This has allowed to point out both the reversibility, the formal potential, and the number of electrons involved in the electrochemical processes, and to evaluate the effect of the substituents present on the aryl ring. The data collected have been able to furnish a complete picture of electronic distribution and have been supported by DFT calculations.

Our research groups are by long time involved in the study of the reactivity and the pharmacological activity of nitrogen-containing heterocyclic compounds: in this line we have now examined the behaviour of some substituted 4- and 7-nitroindazoles. Considering the fact that nitroreduction processes are often essential steps for the biological activity of nitro compounds and remembering that some nitroindazoles show interesting biological activities, we have collected nuclear magnetic resonance, electron spin resonance, and cyclic voltammetry data and carried out density functional theory computations on the above compounds thus obtaining an accurate picture of electronic distribution and reduction processes of the examined substrates as a function of their chemical structure. Looking also to our previous results obtained examining the behaviour of 5- and 6-nitroindazoles, we have confirmed the different general behaviour of 1- and 2-alkyl substituted nitroindazoles strictly related to the known different electronic distribution in these two classes of compounds. Interestingly, cyclic voltammetry data have confirmed the ability of N-1H nitroindazoles to give rise to the formation of dimers, already observed by us studying 5- and 6-nitroindazoles.