A CORRELATION OF REACTION RATES
A CORRELATION OF REACTION RATES
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DOI：
10.1021/ja01607a027
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发表时间：
1955-01-01
影响因子：
15
通讯作者：
HAMMOND, GS
中科院分区：
文献类型：
--
作者：
HAMMOND, GS
虽然在化学反应的速率和自由能之间没有完全普遍的相关性，但在许多情况下，最稳定的产物是由一系列类似组成的反应物以最快的速率形成的。在某些其他反应中，不太稳定的产物似乎以更快的速率以相当大的规律形成。在后一种情况下，过渡态似乎是以最小量的反应物重组形成的。通过调用一个简单的假设，人们可以决定是否反应物或产品或两者都不是很好的结构模型，用于估计结构变化对过渡态自由能的影响。化学家们长期以来一直被反应速率和化学平衡位置之间缺乏任何普遍的相关性所困扰。在许多情况下，高放热反应非常缓慢，因为所有的变化是如此复杂，以至于转化只能通过至少包括一个吸热阶段的分步过程发生。然而，即使当一步反应，或复杂反应的速率控制步骤，进行比较，它被发现，没有反应的自由能和它们的速率之间的一般关系。然而，有足够数量的这样的一步，或基本的，过程中，观察到一个密切的平行关系之间的速率和均衡（测量或推断），使它成为必要的，这种关系的范围给予仔细考虑。我们已经发现，一个相当简单的假设在相当大程度上有助于估计在给定反应中预期的相关程度。同样的概念导致了对另一类反应的理解，在这些反应中，最终的热力学结果对相对反应速率几乎没有影响。
While there is no completely general correlation between the rates and free energies of chemical reactions there are many instances in which the most stable products are formed at the most rapid rates from a series of similarly constituted reactants. In certain other reactions, the less stable products seem to be formed at the more rapid rates with considerable regularity. In thelatter cases it appears that the transition states are formed with the minimum amount of reorganization of the re-actants. By invoking a simple postulate one can decide whether the reactants or products or neither are good structural models for estimating the influenceof structural variations on the free energies of transition states. Several examples of the application of the postulate are presented.Chemists have long been plagued by the lack of any general correlation between reaction rates and the positions of chemical equilibria. In many in-stances highly exothermicreactions are exceed-ingly slow because the over-all changes are so com-plex that the transformations can only occur by stepwise processes which involve at least one endo-thermic stage. However, even when one-step re-actions, or the rate-controlling steps of complex reactions, are compared it is found that there is no general relationship between the free energies of the reactions and their rates. However, there are a sufficient number of such one-step, or elementary, processes in which a close parallelism is observed between rates and equilibria (either measured or inferred) to render it imperative that the scope of such relationships be given careful consideration. We have found that a rather simple postulate aids considerably in estimating the degree of correlation which is to be expected in a given reaction. The same concept leads to an understanding of another class of reactions in which the ultimate thermodynamic consequences have little influence on relative reaction rates.