Mass Spectra of 3-Alkyl-4-cinnolinecarbonitriles

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Mass spectra (MS) of 3-alkyl-4-cinnolinecarbonitrile (I) were examined. In MS of I, (M-·H)⁺ species are encountered only to a minor extent in the lower one in contrast with (M-·N₂H)⁺ species. In particular it is worth noting that (M-·H)⁺ species are not found in MS of 3-methy1-(Ib) and 3-ethyl-4-cinnolinecarbonitrile (Ic). When the alkyl substituent at the 3-position of I such as methyl (Ib), ethyl (Ic), and propyl (Id), is not so bulky, the important fragmentation arises from the initial expulsion of ·N₂H radical from M⁺. In turn, when the alkyl substituent is bulkier than that of isopropyl, the importance of this process is not recognized as seen in MS of 3-isopropyl-(Ie) and 3-butyl-4-cinnolinecarbonitrile (If). Those facts mentioned above mean that the ring cleavage of I by the initial expulsion of ·N₂H radical is dependent on the relative size of the alkyl substituent at the 3-position.