Solvolysis of 2-aryl-exo-5,6-trimethylene-2-norbornyl p-nitrobenzoates as a reference of 2-aryl-2-norbornyl p-nitrobenzoates solvolysis

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 ( 6 8 ) 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 ( 5 7 ) can also be regarded as invariant over the reactivity range studied. The exo/endo rate ratios ( 7 8 ) 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 5 6 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.