MASS SPECTROMETRIC STUDIES OF STRUCTURAL ISOMERS .I. MONO- AND BICYCLIC C7H12 MOLECULES

The mass spectra, metastable transitions, and the appearance potentials of several ions have been obtained for four monocyclic and two bicyclic C7H12 isomers. The molecular ionization potentials determined by the energy distribution difference (EDD) technique are: 8.67 ± 0.02, 8.94 ± 0.03, 8.92 ± 0.02, 9.04 ± 0.03, 9.93 ± 0.02, and 9.03 ± 0.02 eV for 1-methylcyclohexene, 3-methylcyclohexene, 4-methylcyclohexene, methylenecyclohexane, bicyclo[2.2.1]heptane, and bicyclo[4.1.0]heptane, respectively. It is shown that these ionization potentials are dependent upon structural features of the isomeric molecules, e.g., double-bond substitution and ring strain. The differences between the calculated heats of formation for the gaseous parent molecule ions are discussed in terms of the structural differences between the original molecules. Heats of formation for fragment ions indicate that ionization-fragmentation usually produces the same ionic species independent of the original molecules. © 1968, American Chemical Society. All rights reserved.