Tsuji Y, Mori T, Richard J P, Amyes T L, Fujio M, Tsuno Y
Department of Biochemistry and Applied Chemistry, Kurume National College of Technology, Komorinomachi, Kurume 830-8555, Japan.
Org Lett. 2001 Apr 19;3(8):1237-40. doi: 10.1021/ol015706s.
[reaction: see text]. The sum of the rate constants for solvolysis and 18O-scrambling of 4-MeC6H4(13)CH(Me)18OC(O)C6F5 in 50/50 (v/v) trifluoroethanol/water, k(solv) + k(iso) = 1.22 x 10(-5) s(-1), is larger than k(solv) = 1.06 x 10(-5) s(-1) for solvolysis of the unlabeled ester. This shows that the ion pair intermediate undergoes significant internal return. The data give k(-1) = 7 x 10(9) s(-1) for internal return by unimolecular collapse of the ion pair, which is significantly larger than k(Nu) = 5 x 10(8) M(-1) x s(-1) for bimolecular nucleophilic addition of carboxylate anions to 4-MeC6H4CH(Me)+.
[反应：见正文]。在50/50（体积比）三氟乙醇/水体系中，4 - 甲基苯基(13)C(甲基)18O - C(羰基)C6F5的溶剂解速率常数与18O重排速率常数之和，k(solv) + k(iso) = 1.22×10⁻⁵ s⁻¹，大于未标记酯的溶剂解速率常数k(solv) = 1.06×10⁻⁵ s⁻¹。这表明离子对中间体发生了显著的内部返回。数据给出离子对单分子坍塌导致内部返回的k(-1) = 7×10⁹ s⁻¹，这显著大于羧酸根阴离子与4 - 甲基苯基 - C(甲基)⁺进行双分子亲核加成的k(Nu) = 5×10⁸ M⁻¹·s⁻¹。
