GAS-PHASE SUBSTITUTION-REACTIONS BY RADICAL CATIONS .3. METHYLENE TRANSFER OF THE C-C RING-OPENED OXIRANE RADICAL-CATION TO PYRAZOLE AND IMIDAZOLE

In the chemical ionization source of a mass spectrometer the C-C ring-opened oxirane radical cation transfers a methylene group to imidazole and pyrazole. The structures of the [M + 14].+ reaction product ions and those of the ionized methylpyrazole and methylimidazole isomers have been established by collisionally induced dissociation (CID) spectrometry. The methylene transfer reaction of oxirane to pyrazole and imidazole yields 1-methylene-2H-pyrazolium and 1-methylene-3H-imidazolium alpha-distonic radical cations, respectively. Their relative stabilities, and those of three other possible isomeric alpha-distonic product ions, have been calculated by ab initio methods at the #UHF/6-31G//3-21G level of theory.