Gas-Phase Polar Cycloaddition Reactions

Abstract

The ion-molecule reaction chemistry of simple alkenes has been extensively studied in many laboratories. At low ion translational energies, as found in the cell of an ion cyclotron resonance spectrometer, the reactions undoubtedly proceed via an intermediate complex. Although much is known about the product distributions and rates of reaction of these processes, little is known about the structure(s) of the intermediate. This is a difficult question because, in many cases, the intermediate cannot be observed. Its properties can be only inferred by indirect methods such as studies involving isotopic labels or comparison of fragmentation channels with the mass spectral decomposition of suspected intermediate. Unfortunately, deuterium labelling in simple hydrocarbon systems is not very informative because of extensive isomerizations of hydrogen atoms in the intermediate complex prior to subsequent fragmentation.