Analytical Applications of Ion-Molecule Reactions Identification of C₅H₁₀ Isomers by Ion Cyclotron Resonance Spectrometry

Isomeric olefins and cyclic hydrocarbons are often difficult to analyze by conventional mass spectrometry. For this reason, the ion-molecule chemistry of the 1,3 butadiene radical cation and various C₅H₁₀ isomers was investigated with the hope of turning up differences which might be used in the complete identification of such similar compounds. The 1,3-butadiene radical cation produced at 10.9 eV reacts with 1-pentene, 3-methyl-l-butene, 2-methyl-1-butene, and as- and trans-2-pentene to produce C₈H₁₃⁺, C₇H₁₂⁺, C₇H₁₁⁺, C₆H₁₀^-, and C₆H₉⁺. Significant quantitative differences in the ion-molecule chemistry allow each isomer to be distinguished. The other isomeric pentene, 2-methyl-2-butene undergoes only a charge exchange reaction with the butadiene radical cation. The final C₅H₁₀ studied, cyclopentane, is totally inert toward the butadiene radical cation. The results indicate that ion-molecule reactions studied by ICR may prove to be an important complement to conventional mass spectrometry for such difficult analyses.