The r.f.-only-mode event for ion-chemistry studies in fourier transform mass spectrometry: the reactions of propene and cyclopropane radical cations with neutral ethene

The C₅H₁₀ adduct ions from the two highly exothermic reactions of propene (C₃H₆) radical cations with neutral ethene (C₂H₄) and cyclopropane radical cation with ethene were isolated and detected by incorporating an r.f.-only-mode event into the FTMS experimental sequence. These adducts, which cannot be observed under the low-pressure conditions of the normal FTMS experiment, were characterized by comparing their bimolecular reactivity with 1,3-butadiene (C₄H₆) with that of C₅H₁₀ ions formed by ionization of reference compounds. The C₉H₁₆ adducts that originate from all the sources studied here have similar structures that fragment to give product ions of nearly identical relative abundances. Small but real differences are found in the rate constants for most of these reactions, and the differences are interpreted to signify different structures for the adducts that are formed in the actions of ethene with the propene and cyclopropane radical cations. In the case of the propene radical cation reaction, the final product is the highly stable 2-methyl-2-butene radical cation.