STRUCTURE OF THE INTERMEDIATE FORMED IN THE REACTION OF THE STYRENE RADICAL CATION AND NEUTRAL STYRENE.

Article abstract of DOI:10.1021/ja00315a013

The structure of the ion-molecule adduct produced in the gas-phase reaction of the styrene radical cation with neutral styrene has been probed by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition (CAD) spectrum with a tandem mass spectrometer. The CAD spectrum of the adduct is nearly identical with the CAD spectra of the cis- and trans-diphenylcyclobutane radical cations and with the product ion resulting from a 1,4-regiospecific water elimination from the 1,4-diphenylbutan-1-ol radical cation; therefore the radical cations from all four precursors possess the same structure. The DELTA H//f of this radical cation is shown to be less than equivalent to 239 kal/mol; therefore it cannot have the trans-1,2-diphenylcyclobutane structure ( DELTA H//f equals 247 kcal/mol). The results support a two-step mechanism for the left bracket 1 plus 2 right bracket cycloaddition reaction.