A theoretical analysis of the reactions of four N7-protonated purine bases with phenylnitrenium and 4-biphenylylnitrenium ions, both in the gas phase and in aqueous solution, is studied to elucidate the effect of protonated purines on the formation of C8 adducts in a series of complicated carcinogenic reactions. Based on this analysis, four important conclusions are drawn. (i) The mechanism of C8 adduct formation by the addition of arylnitrenium ions directly to C8 sites of nucleotide bases in DNA is still supported. (ii) The N7 protonation of purine bases will lower the rate constants of these carcinogenic reactions, which agrees with observations and proves the experimental presumption. (iii) More complicated arylnitrenium ions have more of an effect on the reduction in the rate constants of these reactions involving N7-protonated purine bases. (iv) The rate constant of the C8 deprotonation process becomes larger when N7-protonated purine bases are involved in these carcinogenic reactions.