Bicyclobutonium ion versus cyclopropylcarbinyl cation chemistry: the cycloaddition reaction with ethene in the dilute gas phase

The C4H7+ cations were formed from cyclopropylcarbinyl, cyclobutyl and homo allyl chlorides via chloride atom loss from the radical cations in a chemic al ionization source. Their structures were probed on a short time-scale (o f the order of 10(-6) s) as a function of internal energy by utilizing coll isionally activated dissociation with tandem mass spectrometric methods. Th e results show that the radical cations of cyclopropylcarbinyl and homoally l chlorides generate primarily the cyclopropylcarbinyl cation, 3, whereas t he radical cation of cyclobutyl chloride generates a substantial amount of bicyclobutonium ion, 4. Ion 4 reacts with nucleophiles via multiple competi ng reaction pathways, unlike 3. Ion 3 undergoes a cycloaddition reaction wi th ethene to generate the cyclopentylcarbinyl cation. Ion 4, although react ive with ethene, does not generate, to any appreciable degree, the cyclopen tylcarbinyl cation. Copyright (C) 2000 John Wiley & Sons, Ltd.