Solvolysis of 2-aryl-exo-5,6-trimethylene-2-norbornyl p-nitrobenzoates as a reference of 2-aryl-2-norbornyl p-nitrobenzoates solvolysis: Further evidence for the unimportance of σ-participation in the solvolysis of 2-aryl-2-norbornyl derivatives |
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Authors: | Kenichi Takeuchi Takeshi Kurosaki Kunio Okamoto |
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Institution: | Department of Hydrocarbon Chemistry, Faculty of Engineering, Kyoto University, Sakyo-ku, Kyoto 606, Japan |
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Abstract: | The rates of solvolysis of 2 - aryl - exo - 5,6 - trimethylene - exo - and endo - 2 - norbornyl p-nitrobenzoates (7 and 8, respectively) with representative substituents p-CH3O, p-CH3, H, m-CF3, p-CF3, and 3,5-(CF3)2] were determined in 80% aqueous acetone and compared with those of the parent 2-aryl-exo- and endo-2-norbornyl p-nitrobenzoates (5 and 6, respectively). The rate ratios for the endo-p-nitrobenzoates () are essentially constant and close to unity for these substituents, indicating that the perturbation of the trimethylene bridge toward the C2-position is virtually negligilbe. The rate ratios for the exo-p-nitrobenzoates () can also be regarded as invariant over the reactivity range studied. The exo/endo rate ratios () are 246 (p-CH3O), 196 (P-CH3), 129 (H), 80 (m-CF3), 90 (p-CF3), and 89 3,5-(CF3)2], being similar to the corresponding rate ratios. The solvolyses of these p-nitrobenzoates (7 and 8) afford predominantly ( > 97%) exo-alcohols. Since the secondary exo-5,6-trimethylene-2-norbornyl system, with its low exo/endo rate ratio, 11.2, is known to solvolyse without significant σ-participation, the tertiary derivatives should also undergo solvolysis without σ-participation. Consequently, the similarities in the solvolytic behaviors between the two systems (5 vs 7; 6 vs 8) strongly support the previous conclusion that σ-participation is unimportant in the solvolysis of 5. |
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