CHARGED PHENYL RADICALS

The chemical properties of phenyl radicals with different chemically i nert charged substituents in the ortho, meta, and para positions were examined in the gas phase in a Fourier-transform ion cyclotron resonan ce mass spectrometer. The radicals were generated by replacing a chlor ine, bromine, or iodine atom in a radical cation of dihalobenzene with a nucleophile and by cleaving the remaining iodine or bromine atom by collision-activated dissociation. The radicals' structures were chara cterized by ion-molecule and dissociation reactions and by comparison to the reactivity of isomeric reference ions. Ab initio molecular orbi tal calculations (ROMP2/6-31G//ROHF/6-31G* + ZPE) carried out for the 2-, 3-, and 4-dehydrophenylsulfonium ions suggest that these three sp ecies are nearly equal in energy and significantly less stable than th e isomeric thiophenol radical cation. Most of the charge density is lo calized on the substituent in the charged phenyl radicals examined com putationally. The odd-spin density at the radical site is calculated t o be the same as in the neutral phenyl radical. These computational re sults predict chemical properties drastically different from those typ ical for conventional organic radical cations, e.g., the radical catio n of thiophenol. This was found to be the case. Phenyl radicals with d ifferent charged groups in the meta or para position yield the same re action products as the neutral phenyl radical (the ortho isomers rearr ange upon collisions). Further, charged and neutral phenyl radicals sh ow similar reactivity trends toward different substrates. Examination of the reactivity of radicals of various sizes and with the charged gr oup in different locations with respect to the radical site suggests t hat the reaction efficiency toward a given substrate is predominantly determined by the electron deficiency at the reacting radical site. Al l these findings parallel those reported earlier for neutral phenyl ra dicals, and suggest that phenyl radicals with a chemically inert charg ed substituent in a remote position provide a useful model for the exa mination of the properties of neutral phenyl radicals in the gas phase .