Use of Kinetic Isotope Effects in Mechanism Studies. 5.<sup>1</sup> Isotope Effects and Element Effects Associated with Hydron-Transfer Steps during Alkoxide-Promoted Dehydrohalogenations
作者:Heinz F. Koch、Gerrit Lodder、Judith G. Koch、David J. Bogdan、Geoffrey H. Brown、Carrie A. Carlson、Amy B. Dean、Ronald Hage、Patrick Han、Johan C. P. Hopman、Lisa A. James、Petra M. Knape、Eric C. Roos、Melissa L. Sardina、Rachael A. Sawyer、Barbara O. Scott、Charles A. Testa、Steven D. Wickham
DOI:10.1021/ja970189n
日期:1997.10.1
halide, . Isotope effects at 25 °C for I, (kH/kD)Obs = 3.40 and (kH/kT)Obs = 6.20, and II, (kH/kD)Obs = 3.49 and (kH/kT)Obs = 6.55, result in similar values for a: aH = 0.59, aD = 0.13−0.14 and aT = 0.07. Smaller values of (kH/kD)Obs = 2.19 and (kH/kT)Obs = 3.56 for III are due to more internal return [aH = 1.9, aD = 0.50, and aT = 0.28] associated with the dehydrofluorination reaction. Calculation of k1
主要动力学同位素效应 (kH/kD)Obs 和 (kH/kT)Obs 的 Arrhenius 行为,与甲醇钠促进的 m-ClC6H4CiHClCH2Cl (I)、m-CF3C6H4CiHClCH2Cl (II) 和 p- CF3C6H4CiHClCH2F (III) 已被用于计算内部返回参数 a = k-1/ ,采用氢键碳负离子的两步机制。这种碳负离子在将氢返回碳 k-1 和卤化物损失之间分配。同位素效应在 25 °C 时对 I (kH/kD)Obs = 3.40 和 (kH/kT)Obs = 6.20,以及 II (kH/kD)Obs = 3.49 和 (kH/kT)Obs = 6.55,导致a 的相似值:aH = 0.59,aD = 0.13−0.14 和 aT = 0.07。III 的 (kH/kD)Obs = 2.19 和 (kH/kT)Obs = 3.56 的较小值是由于与脱氟化氢反应相关的更多内部回报