Rate constants for the proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to cesium n-propoxide in n-propanol have been measured under pseudo-first-order conditions with an excess of base for four temperatures between 5 and 35 °C. Using literature values of the fraction of cesium n-propoxide ion pairs that are dissociated into free ions, separate second-order rate constants for the proton and deuteron transfer to the ion pair and to the free ion have been calculated. The cesium n-propoxide ion pair is about 2.8 times more reactive than the free n-propoxide ion. The primary kinetic isotope effects for the two reactions are the same (kH/kD = 6.1–6.3 at 25 °C) within experimental error. The enthalpy of activation is smaller for the ion-pair reaction and the entropy of activation more negative than for the free-ion reaction. For proton transfer, ΔH±ion pair = 8.3 ± 0.2 kcal mol−1, ΔH±ion = 9.6 ± 1.0 kcal mol−1, ΔS±ion pair = −12.3 ± 0.6 cal mol−1 deg−1, ΔS±ion = −10.1 ± 3.4 cal mol−1 deg−1. The greater reactivity of the ion pair relative to the free ion is interpreted in terms of the weaker solvation shell of the ion pair in the initial state.
在过量碱的情况下,测量了1-(4-硝基苯基)-1-硝基乙烷对正丙醇中的氢质子和氘质子转移到正丙氧化铯的速率常数,在5°C和35°C之间进行了伪一级条件下的四个温度的测量。利用文献值计算了铯丙氧化物离子对分解为自由离子的分数的二阶速率常数,分别用于质子和氘质子转移到离子对和自由离子。铯丙氧化物离子对比自由丙氧化铯离子反应活性大约高2.8倍。两个反应的主要动力学同位素效应相同(在25°C下kH/kD = 6.1-6.3),在实验误差范围内。离子对反应的活化焓较小,活化熵比自由离子反应更负。对于质子转移,ΔH±ion pair = 8.3 ± 0.2 kcal mol-1,ΔH±ion = 9.6 ± 1.0 kcal mol-1,ΔS±ion pair = -12.3 ± 0.6 cal mol-1 deg-1,ΔS±ion = -10.1 ± 3.4 cal mol-1 deg-1。离子对相对于自由离子的更高反应活性是由于初始状态下离子对的溶剂化壳较弱。