Reinvestigation of the linear free energy relationship on the solvent effects in the solvolysis of arylalkyl tosylates

Winstein-Grunwald方程log(k/k_o)=My+1N已被广泛用作分析溶积过程的机械探针。尽管芳基辅助和苄基溶剂具有亲核限制的性质，但溶剂效应对这些溶剂的影响不能与金刚烷基Y&lt；Ots&gt；参数线性相关，而是在不同的二元水溶剂系列中表现出特征分散。分散的模式不能简单地用亲核溶剂辅助来解释。与脂肪族定域2-金刚烷基阳离子相比，苯基k_c碳阳离子过程过渡态反应中心的显影电荷通过与芳基的有效PI重叠而高度离域，这可能导致反应中心高度定向的比溶剂化的损失。详细考察了最适用于芳基辅助溶解的电离功率标度，并与基于2-烷基对甲苯磺酸盐溶解的Y&lt；Ots&gt；溶剂标度进行了比较。基于对甲氧基新叶酸溶剂分解的溶剂极性标度Y&lt；Delta&gt；与基于2-金刚烷基酮的溶剂极性标度Y_&lt；Ots&gt；相结合，对含有不同程度PI离域作用的苯基芳基烷基对甲苯磺酸盐的溶剂化表现出广泛的适用性：log(k/k_o)=ay&lt；Ots&gt；+by&lt；Delta&gt；通过Y&lt；Ots&gt；和Y&&lt；Delta&gt；的线性组合，可以将苯基溶质处理为极高精度的R&gt；0.995和SD&lt；0.15。修正的方程ay&lt；Ots&gt；和包括CN&lt；Ots&gt；项的应用也已扩展到烷基和芳基对甲苯磺酸盐的亲核溶液，但成功有限，表明亲核溶剂的参与没有精确的可加性。

The Winstein-Grunwald Equation, log (k/k_o) = mY + 1N, has been widely used as a mechanistic probe for analyzing the solvolytic processes. Despite the nucleophilically limiting nature of aryl-assisted and benzylic solvolyses, the solvent effect on these solvolyses failed to give a single linear correlation with the adamantyl Y_<OTs> parameter but showed characteristic dispersion for various binary aqueous solvent series. The pattern of dispersion can not be explained by simply Invoking the nucleophilic solvent assistance. Developing charge at the reaction center in the transition state of benzylic k_c carbocationic process is highly delocalized through effective PI-overlapping with aryl group, and this may cause a significant loss of the highly oriented specific solvation at the reaction center In comparison with that for aliphatic localized 2-adamantyl cation.Detailed examination of ionizing power scale most suitable to the aryl-assisted solvolysis as well as to the benzylic solvolyses, has been carried out in the comparison with the Y_<OTs> solvent scale based on the solvolysis of 2-adamantyl tosylate. The solvent polarity scale Y_<DELTA> based on p-methoxyneophyl solvolysis combined with the Y_<OTs> based on 2-adamantyl one has been found to show wide applicability to the solvolyses of benzylic arylalkyl tosylates involving varying degree of PI-delocalization interaction with the incipient carbocation charge ; log (k/k_o) = aY_<OTs> + bY_<DELTA>. Benzylic solvolyses can be treated to an extremely high precision R>0.995 and SD<0.15 with linear combination of Y_<OTs> and Y_<DELTA>. Application of revised equation, aY_<OTs> and bY_<DELTA> Including cN_<OTs> term has also been extended to the nucleophilic solvolyses of alkyl and arylalkyl tosylates, with limited success, indicating no precise additivity for the nucleophilic solvent involvement.