Evidence of reversible addition of carbon-centered radicals to aromatic nuclei.
Item
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Title
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Evidence of reversible addition of carbon-centered radicals to aromatic nuclei.
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Identifier
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AAI9029941
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identifier
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9029941
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Creator
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Henschel, Rouget Frederick.
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Contributor
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Adviser: Leonard H. Schwartz
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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Radical systems catalyze the racemization of optically active methyl 2,2{dollar}\sp\prime{dollar}-dicarboxy-9,9{dollar}\sp\prime{dollar}-bianthryl (11). The racemization is inhibited by hydrogen donors. The optical activity of 11 is due to restricted rotation around the carbon-carbon bond linking the two aromatic rings. It is suggested that the racemization is catalyzed by the reversible formation of a sigma-complex addition intermediate which has a lower rotational barrier compared to the aromatic substrate. The Arrhenius parameters for the thermal racemization of 11 in bromobenzene have been determined.;Radical-catalyzed racemization of 11 has been observed previously, however the identity of the radical or radicals responsible was uncertain because solvent radicals were also formed. Racemization of 11 in the presence of dibenzylmercury, a thermal source of benzyl radicals, was investigated in two inert solvents, bromobenzene and tert-butylbenzene. Racemization of 11 was accompanied by very little product formation. Both solvents were shown to be inert to benzyl radical. It is concluded that racemization of 11 is exclusively due to reversible addition of benzyl radical.;Diisopropylmercury and diethylmercury were used as thermal sources of isopropyl and ethyl radicals, respectively. The half-lives of diethylmercury (at 200{dollar}\sp\circ{dollar}C) and diisopropylmercury (at 170{dollar}\sp\circ{dollar}C) were established in bromobenzene. The kinetic order was determined for the racemization of 11 by diethylmercury and diisopropylmercury in bromobenzene. Azoisopropane and azoethane were used as alternative sources of isopropyl and ethyl radicals. Both catalyzed the racemization of 11 when heated in bromobenzene.;Attempts to catalyze the racemization of dimethyl 6,6{dollar}\sp\prime{dollar}-dinitrobiphenyl-2,2{dollar}\sp\prime{dollar}-dicarboxylate (3), dineopentyl 6,6{dollar}\sp\prime{dollar}-dinitrobiphenyl-2,2{dollar}\sp\prime{dollar}-dicarboxylate (4), and dimethyl 4,4{dollar}\sp\prime{dollar},6,6{dollar}\sp\prime{dollar}-tetranitrodiphenate (5) in the presence of nucleophiles were unsuccessful.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
