The chemistry of selected carbene and radical ion intermediates

Selected reactive intermediates were studied using experimental and theoretical methodology. Irradiation in the presence of electron transfer agents triethylamine, 1,4-diazobicyclo[2.2.2]octane and quinuclidine each gave two mono-defluorination products: 1,2,3,5 and 1,2,4,5-tetrafluorobenzene. The mechanistic formation of the mono-defluorination products is discussed in terms of the respective product ratios.;Carbene generation by pyrolytic decompostition of the Li salt of the tosylhydrazone of 4,4-diphenyl-2,5-cyclohexadienone produces a mixture of products which includes o-terphenyl. C13 labeling studies and semi-empirical AM1 molecular orbital calculations elucidate the mechanistic pathway for the formation of o-terphenyl. A single mechanism is involved which proceeds through formation of an isobenzene species followed by subsequent phenyl and hydrogen migrations.;Rearrangement of bivalent 2-carbenabicyclo[3.2.1]octa-1,6-diene to product proceeds via a carbene to carbene rearrangement process to generate endo-6-(2-carbenavinyl)bicyclo[3.1.0]hex-2-ene. Tricyclo[3.2.1]octa-2,3,6-triene and 3-carbenatetracyclo[3.3.0.02,8 .04,6]octane proceed directly to product. The formation of hydrocarbons bicyclo[3.2.1]octa-2,6-diene, tricyclo[3.2.1.02,7]oct-3-ene and tetracyclo[3.3.02,8.04,6]octane from 2-carbenabicyclo[3.2.1]octa-2,6-diene was also investigated, and can be explained by a combination of a singlet diradical rearrangement and triplet 2-carbenabicyclo[3.2.1]octa-2,6-diene.;The C7 carbene in 7-carbenanorbornene and the C8 carbene center in 8-carbenaendotricyclooctane are strongly bent towards the double bond and cyclopropane ring, respectively, in contrast to their related triplets and parent hydrocarbons. The geometric change for singlet 3-carbenabicyclohexane compared to the triplet or to parent bicyclo[3.1.0]hexane is minimal. 2-Carbenanorbornene gave evidence of very modest bridging. The stabilization energy and geometry of 2-carbenabicyclooctadiene resemble an antihomoaromatic bicyclooctadienyl cation rather than the related homoaromatic bicyclooctadienyl anion. The singlet-triplet energy differences for each of the respective species is also evaluated. (Abstract shortened by UMI.).