HIGH-PRESSURE PHOTIONIZATION MASS SPECTROMETRY .1. UNIMOLECULAR AND BIMOLECULAR REACTIONS OF C4H8+ FROM CYCLOBUTANE

Various mixtures of cyclobutane with cyclohexane, methylcyclopentane, 2-methylpentane, and cyclopentane have been selectively photolyzed at either 1236 Å (10.0 eV) or 11.65 Å (10.6 eV) in a mass spectrometer designed to provide specific information concerning thermal ion-molecule reactions occurring in the gas phase. The modes of reaction as well as the total reactivity found for C4H8+ from cyclobutane in mixtures with the various hydrocarbons have been compared with those determined for 1-C4H8+, i-C4H8+, and 2-C4H8+ ions produced by photoionization of the appropriate butene at 10.0 eV. Evaluation of these data, including the charge exchange pattern for C4H8+ established by the addition of compounds with various ionization potentials (NO, trimethylamine, cyclohexane, etc.), indicate that the C4H8+ ion from cyclobutane is noncyclic and that two or more different open-ring structures may coexist. The reaction c-C6H12+ + c-C4H8 ⇅ C6H12 + C4H8+, where c-C6Hi2+ is produced by photoionization of cyclohexane at 10.0 eV, has also been found. The interesting feature of this process is that charge exchange is exothermic on the basis of current ΔHf values only if C4H8+ acquires a butene ion structure during the lifetime of the collision complex. © 1969, American Chemical Society. All rights reserved.