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Characterization of Transition State based on Solvation Behavior

基于溶剂化行为的过渡态表征

基本信息

批准号：
06453041
负责人：
TSUNO Yuho
金额：
$ 5.38万
依托单位：
KUMAMOTO UNIVERSITY (1995)Kyushu University (1994)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

The solvent effect on these solvolyses of aryl-assisted and benzylic solvolyses, despite the nucleophilically limiting nature, generally failed to give a single linear correlation with the Winstein-Grunwald Equation, using the adamantyl Y_<OTs> but showed characteristic dispersion for various binary aqueous solvent series. It is evident that developing charge at the reaction center in the transition state of benzylic k_c carbocationic process is highly delocalized through effective PI-overlapping with the aryl group, and this may cause a singificant loss of the highly oriented specific solvation at the charge-delocalized reaction center in comparison with that for aliphatic localized 2-adamantyl cation. The solvent polarity scale YDELTA based on p-methoxyneophyl solvolysis combined with the Y_<OTs> has shown a wide applicability to the solvolyses of benxylic arylalkyl tosylates involving varying degree of PI-delocalization interaction with the incipient carbocation charge ; log (k/k_O) = aY_<OTs> +bYDELTA. The equation can be applied to a series of aryl-assisted solvolyses in an extremely high precision, suggesting a continuous spectrum of k_c - kDELTA mechanisms. Benzylic k_c solvolyses can also be treated with linear combination of Y_<OTs> and YDELTA. Application of above generalized equation, including cN_<OTs> term, has also been extended to the nucleophilic solvent assisted solvolyses of alkyl and arylalkyl tosylates, e.g., for a series of substituted benzyl tosylates with limited success, particularly indicating no precise additivity (or non-linearity) for the nucleophilic solvent assistance.

溶剂对芳基辅助溶剂解和苯基溶剂解的影响，尽管具有亲核限制性质，但在使用刚玉基Y_<OTs>时，通常不能与Winstein-Grunwald方程建立单一的线性关系，但在各种二元水溶液系中表现出特征的分散。很明显，在苯基k_c碳阳离子过程的过渡态中，通过与芳基的有效pi重叠，在反应中心形成电荷是高度离域的，这可能导致在电荷离域的反应中心高度定向的比溶剂化的显著损失，而在脂肪族定域的2-adamantyl阳离子中则是如此。基于对甲氧基新叶酚溶剂解与Y_<OTs>相结合的溶剂极性标度YDELTA广泛适用于苯基芳烷基甲酯的溶剂解，涉及不同程度的pi离域与初始碳正离子电荷的相互作用；log (k/k_O) = aY_<OTs bb_0 +bYDELTA。该方程可以应用于一系列芳基辅助溶剂分解，具有极高的精度，表明k_c - kDELTA机理具有连续谱。Y_<OTs>和YDELTA的线性组合也可以处理苯基k_c溶剂解。上述广义方程的应用，包括cN_<OTs>项，也已推广到亲核溶剂辅助下烷基和芳基烷基苯磺酸盐的溶剂解，例如，一系列取代苯磺酸盐的成功有限，特别是表明亲核溶剂辅助没有精确的可加性（或非线性）。