Nueleophilicities of nitroalkyl anions
Nueleophilicities of nitroalkyl anions
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DOI：
10.1021/jo048773j
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发表时间：
2004-10-29
影响因子：
3.6
通讯作者：
Mayr, H
中科院分区：
文献类型：
--
作者：
Bug, T;Lemek, T;Mayr, H
用光度法研究了八种硝基烷基阴离子（硝酸根阴离子）与二苯甲基鎓离子和醌甲基化物在DMSO和水中的反应动力学。的二阶速率常数被发现遵循里奇常数的选择性关系，选择性略小于以前观察到的其他碳负离子和O或N亲核试剂。通过相关方程log k（20 ℃）= s（N + E）对动力学数据进行评估，得到亲核性参数（N），其允许将硝基膦酸盐的亲核性与其他类别化合物的亲核性进行比较。尽管在DMSO中脂族硝膦酸酯la-c比芳族代表Id-h更亲核，但水合使脂族硝膦酸酯的亲核性降低了1百万倍，这显著大于芳族硝膦酸酯的反应性的降低，结果是芳族硝膦酸酯在水中比脂族硝膦酸酯更亲核。硝基膦酸盐的亲核反应活性在DMSO中受取代基变化的影响很小，在水溶液中受取代基变化的影响更小，这被认为是不寻常的速率平衡关系的原因，即所谓的硝基烷烃异常。外层电子转移不发生在任何的反应进行了研究。
The kinetics of the reactions of eight nitroalkyl anions (nitronate anions) with benzhydrylium ions and quinone methides in DMSO and water were investigated photometrically. The second-order rate constants were found to follow a Ritchie constant selectivity relationship with slightly smaller selectivities than those observed previously for other carbanions and O or N nucleophiles. Evaluation of the kinetic data by the correlation equation log k (20 degreesC) = s(N + E) yields the nucleophilicity parameters, (N), which allow a comparison of the nucleophilicities of nitronates with those of other classes of compounds. Although the aliphatic nitronates la-c are more nucleophilic than the aromatic representatives Id-h in DMSO, hydration reduces the nucleophilicities of aliphatic nitronates by a factor of 1 million, which is considerably greater than the reduction of the reactivities of the aromatic nitronates with the consequence that aromatic nitronates are more nucleophilic in water than aliphatic ones. The nucleophilic reactivities of nitronates are only slightly affected by substituent variation in DMSO and even less so in aqueous solution, which is considered to be the reason for the unusual rate equilibrium relationships, the so-called nitroalkane anomaly. Outersphere electron transfer does not occur in any of the reactions that were investigated.