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8111762 
Journal Article 
Mechanisms of Elimination Reactions. V. Preparation and Elimination Reactions of cis- and trans-11,12-Dichloro-9,10-dihydro-9,10-ethanoanthracene 
Cristol, SJ; Hause, NL 
1952 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
74 
9 
2193-2197 
English 
Previous work has indicated the stereochemical preference for trans elimination of the elements of hydrogen halides in second-order alkaline dehydrohalogenation reactions of alkyl halides. In a continuation of a study of cis and trans elimination, work with the cis-trans isomers of 11,12-dichloro-9,10-dihydro-9,10-ethanoanthracene was undertaken. The isomeric compounds were prepared by diene syntheses involving anthracene with cis- and trans-dichloroethylenes. Each of the isomers gave 9,10-dihydro-9,10-ethenoanthracene when treated with sodium in isopropyl alcohol or with zinc in ethyl alcohol. The structure of the olefin was confirmed by hydrogenation to the known 9,10-dihydro-9,10-ethanoanthracene. These results show that the trans-configuration of halogen substituents is not required for the elimination of halogen from α,β-dihalides with metals. Each isomer was shown to give 11-chloro-9,10-dihydro-9,10-ethenoanthracene on treatment with ethanolic alkali. A kinetic study has been made of the dehydrochlorination of each of the cis-trans-dichlorides with sodium hydroxide in a water-ethanol-dioxane solution at four different temperatures (30° range) for each isomer. The trans-dichloride (cis-hydrogen and chlorine atoms) unexpectedly reacted seven to nine times faster than the cis-dichloride (trans-hydrogen and chlorine atoms). To the best of our knowledge, there are no analogous results reported in the literature. This preference in rate for cis elimination was found to be entirely due to a favorable entropy of activation (and to the relatively high temperature required for reaction), as trans elimination was favored by four kilocalories per mole in activation energy. These results are discussed in terms of a planar transition state for the one-stage elimination process. © 1952, American Chemical Society. All rights reserved.