Cyclopropane as a propagating reagent in gas-phase radical cation oligomerization

Fourier transform (FTMS), collisionally activated dissociation, and tandem mass spectrometry, were utilized for investigating gas-phase radical-cation initiated reactions where neutral cyclopropane functions as the propagating reagent. When cyclopropane is reacted in a FTMS trap with the radical cations of ethylene, propylene, and cyclopropane as initiators, the cyclopropane propagating species undergoes successive reactions that proceed by the addition of three carbons followed by the rapid expulsion of ethylene, resulting in the sequential addition of a methylene unit. The mechanism of these successive addition reactions, whereas potentially being either radical- or cation-based, is consistent with a cationic addition processes. The resulting radical cations that now contain an additional methylene unit addition undergo extensive isomerization. The isomerized species may react further with the cyclopropane propagating reagent to yield higher-order oligomeric radical cations. With the cyclopropane radical cation as the initiator, neutral cyclopropane adds, in successive reactions, three methylene units resulting in a mixture of C₆H₁₂^·+ ions, the highest-order oligomeric products observed. These ions do not react further with cyclopropane, hence causing the oligomerization process to stop.