THE ELEMENT EFFECT AS A CRITERION OF MECHANISM IN ACTIVATED AROMATIC NUCLEOPHILIC SUBSTITUTION REACTIONS
THE ELEMENT EFFECT AS A CRITERION OF MECHANISM IN ACTIVATED AROMATIC NUCLEOPHILIC SUBSTITUTION REACTIONS
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DOI：
10.1021/ja01559a040
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发表时间：
1957-01-01
影响因子：
15
通讯作者：
PRUITT, KM
中科院分区：
文献类型：
--
作者：
BUNNETT, JF;GARBISCH, EW;PRUITT, KM
本文测定了9种1-取代-2，4-二硝基苯与哌啶在甲醇中缩合生成2，4-二硝基苯哌啶的反应速率。三个取代基，氟，硝基和对甲苯磺酰氧基，被取代非常迅速，而六个取代基被取代更慢，在六个之间的速率变化非常小。由于这六个取代基的取代涉及碳与其他五个元素之间的键断裂，因此这一结果表明，键断裂在这些反应的速率决定过渡态中没有取得显著进展。因此，严格的SN 2-样机制被消除，但替代的一步机制没有。然而，事实是最一致的解释，在中间复杂的机制与步骤，其中形成的复合物I是速率决定。这一结果对这些亲核取代反应的意义与Melander观察到的硝化和溴化反应中氢同位素效应的缺乏对这些反应的意义相同。有趣的并发症中遇到的几个反应的研究，但这些并没有阻止令人满意的确定所需的速率系数。
Rates of condensation of nine l-substituted-2, 4-dinitrobenzenes with piperidine in methanol to form 2, 4-dinitrophenylpiperidine (II) have been measured. Three substituents, fluorine, nitro and p-toluenesulf onoxy, are displaced very rapidly while six substituents are displaced more slowly with remarkably little variation in rate amongst the six. Since displace-ment of these six substituents involves the breaking of bonds between carbon and five other elements, this result indicates that bond-breaking has not made significant progress in the rate-determining transition states of these reactions. The strictly SN2-like mechanism is thereby eliminated, but an alternate one-step mechanism is not. However, the facts are most agreeably interpreted in terms of the intermediate complex mechanism with the step in which the complex I is formed being rate determining. This result has the same significance for these nucleophilic substitutions that Melander’s observa-tion of the lack of a hydrogen isotope effect in nitration and bromination had for those reactions. Interesting complications were encountered in several of the reactions studied, but these did not prevent satisfactory determination of the desired rate coefficients.