Is the tert-butyl chloride solvolysis the most misunderstood reaction in organic chemistry?: Evidence against nucleophilic solvent participation in the tert-butyl chloride transition state and for increased hydrogen bond donation to the 1-adamantyl chloride solvolysis transition state
Is the tert-butyl chloride solvolysis the most misunderstood reaction in organic chemistry?: Evidence against nucleophilic solvent participation in the tert-butyl chloride transition state and for increased hydrogen bond donation to the 1-adamantyl chloride solvolysis transition state
复制标题
DOI：
10.1021/ja010600d
复制
发表时间：
2001-11-07
影响因子：
15
通讯作者：
Gajewski, JJ
中科院分区：
文献类型：
--
作者：
Gajewski, JJ
尽管理论计算与此相反，但有人认为在高介电常数介质中，金刚烷基阳离子比叔丁基阳离子更稳定。这一论点已被用来表明叔丁基氯在乙醇水溶液中较高的溶解速率是亲核溶剂参与这一经典反应的证据。此外，在“高度电离”的溶剂中，1-金刚二酰氯的速率几乎与叔丁基氯的速率相同，这被解释为阳离子相对稳定的一种表现。然而，所引用的证据并不能解释1-金刚二酰氯的溶剂溶解率比叔丁基氯对更能提供氢键的溶剂的敏感性增加。这里提出的假设是，1-金刚二酰氯的溶剂解比叔丁基氯的溶剂解更大程度上得益于氢键供能，这很可能是由于在发展中的锥体阳离子中减少了空间相互作用。这一假设得到了多参数溶剂效应因子分析的支持，该分析利用KOMPH2方程，此外，量化了由强溶剂-溶剂相互作用引起的基态不稳定的重要作用。叔丁基氯溶剂溶解过渡态自由转移能的良好相关性的一个重要结果是，即使在非羟基碱性溶剂中，也没有发生机理的变化，特别是没有亲核参与。该方程也适用于二甲磺酸的情况。在离子溶解法中，叔丁基盐在乙醇和气相中的反应速度比1-金刚烷盐快得多。前者在氢键提供溶剂中相对于气相的降低率尚不清楚。为表征溶剂亲核性而产生的溶剂N值与溶剂碱度的度量无关，而是与溶剂氢键供体能力的度量负相关。
Despite theoretical calculations to the contrary, it has been argued that the I-adamantyl cation is more stable than the tert-butyl cation in media of high dielectric constant. This argument has been utilized to suggest that the higher rate of solvolysis of tert-butyl chloride in aqueous ethanol is evidence for nucleophilic solvent participation in this classic reaction. Further, in "more highly ionizing" solvents, the rate of 1-adamantyl chloride is nearly the same as that of tert-butyl chloride, which is interpreted as a manifestation of the relative stabilities of the cations. However, the evidence cited does not explain the increased sensitivity of the rate of solvolysis of 1-adamantyl chloride over tert-butyl chloride to solvents which are better able to donate hydrogen bonds. The hypothesis developed here is that 1-adamantyl chloride solvolysis is assisted by hydrogen bond donation departing chloride ion to a greater extent than that of tert-butyl chloride solvolysis, most likely due to lessened steric interactions in a developing pyramidal cation. This hypothesis is supported by multiparameter solvent effect factor analyses utilizing the KOMPH2 equation which, in addition, quantifies the important role of ground-state destabilization due to strong solvent-solvent interactions. An important result from the good correlation of free energies of transfer of the tert-butyl chloride solvolysis transition state is that there is no change in mechanism, and, in particular, no nucleophilic participation even in non-hydroxylic basic solvents. The equation is also applied to the case of dimethylsulfonium. ion solvolyses where the tert-butyl salt reacts substantially faster than the 1-adamantyl salt in ethanol and the gas phase. The decreased rate of the former in hydrogen bond donating solvents relative to the gas phase is as yet unclear. Solvent N values that were generated to characterize solvent nucleophilicity are shown not to be correlated by measures of solvent basicity but rather by the negative of measures of solvent hydrogen bond donor ability.