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 propagatin g reagent, When cyclopropane is reacted in a FTMS trap with the radical cat ions of ethylene, propylene, and cyclopropane as initiators, the cyclopropa ne propagating species undergoes successive reactions that proceed by the a ddition of three carbons followed by the rapid expulsion of ethylene, resul ting in the sequential addition of a methylene unit. The mechanism of these successive addition reactions, whereas potentially being either radical- o r cation-based, is consistent with a cationic addition processes. The resul ting 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, neu tral cyclopropane adds, in successive reactions, three methylene units resu lting in a mixture of C6H12+ ions, the highest-order oligomeric products ob served. These ions do not react further with cyclopropane, hence causing th e oligornerization process to stop. (C) 2001 Elsevier Science B.V.