Abstract
| - This work describes studies of the electron-promoted Cope cyclization of 2,5-phenyl-1,5-hexadiene radicalanions in a flowing afterglow triple quadrupole mass spectrometer. The electronic properties of thehexadienes have been systematically modified by using aromatic substituents at the 2- and 5-positions ofthe hexedienes, including those with nitro, trifluoromethyl, fluoro, chloro, and acetyl groups. Ions wereformed by the thermal attachment of electrons in the gas phase. Structures of the molecular radical anionswere probed to determine whether they undergo cyclization to a cyclohexane-1,4-diyl anion structure byexamining chemical reactivity with neutral reagents including carbon dioxide, carbon disulfide, and nitricoxide. First-order rate constants for the reactions of ions were measured, and the reaction efficiencieswere determined. Based on the reactivity results, a thermochemical model has been developed, whichpredicts the reaction thermochemistry by using thermochemical properties of model systems. The observedreactivity from ion−molecule reactions and the study of reaction rates show that the ion of2,5-dicyanohexadiene and 2,5-di(4,4‘-trifluoromethyl phenyl)-1,5-hexadiene undergo Cope cyclization,whereas the radical anions having substituents such as the fluoro, nitro, chloro, and acetyl groups do not.
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