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Study of Transition-State Structures of Accelerated Reactions

加速反应过渡态结构的研究

基本信息

批准号：
61470024
负责人：
ANDO Takashi
金额：
$ 3.46万
依托单位：
Shiga University of Medical Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

Transition-state structures of aliphatic nucleophilic substitutions accelerated by electronic effect, solvent effect, phase-transfer catalysts, and neighboring group participation were elucidated by means of kinetic isotope effects of secondary deuterium, primary carbon-13 and -14, and nitrogen-15. Variation in the transition states of the Menschutkin-type alkyl transfer reactions by electronic perturbation of substituents introduced on the nucleophile, leaving group, and alkyl substrate were successfully interpreted by the use of the More O'Ferralltype potential energy surface diagram. Benzyl transfer reaction has more flexible transition state than methyl transfer, presumably because of the greater polarizability of the phenyl group compared with that of hydrogen. Although hydration of nucleophiles in nonpolar solvents with a small number of water molecules slows down the rate of reactions catalyzed by phase-transfer catalysts to a great extent, a-deuterium kinetic isotope effects sh … More owed no indication of considerable changes in the transition-state structure. Acceleration by solvent change also has only subtle effect on the transition-state structure and difficult to interpret. Intramolecular nucleophilic substitutions by neighboring group are important in determining the rate of reactions. Variation in the transition-state structure of these reactions is interpreted in a similar manner as that used for intermolecular nucleophilic substitutions. Acceleration caused by inorganic solid supports in organic solvents becomes maximum by the addition of a trace amount of water. This is attributed to the formation of the "Omega phase", a very polar phase on the inorganic solid, in which nucleophiles are active because of the release from the crystal lattice and insufficient solvation. Taking advantage of this active state, efficient catalytic and noncatalytic reactions by solid base, nucleophilic substitutions, and electrohpilic additions were developed. Selectivity could also be altered in these interfacial reactions. Less

通过仲氘、初级碳13和-14以及氮15的动力学同位素效应阐明了由电子效应、溶剂效应、相转移催化剂和邻近基团参与加速的脂肪族亲核取代的过渡态结构。通过使用 More O'Ferrall 型势能面图，成功地解释了由于亲核试剂、离去基团和烷基底物上引入的取代基的电子扰动而导致的 Menschutkin 型烷基转移反应过渡态的变化。苄基转移反应比甲基转移具有更灵活的过渡态，这可能是因为苯基比氢具有更大的极化性。尽管亲核试剂在非极性溶剂中与少量水分子的水合在很大程度上减慢了相转移催化剂催化的反应速率，但α-氘动力学同位素效应并未表明过渡态结构发生显着变化。溶剂变化引起的加速对过渡态结构也只有微妙的影响并且难以解释。邻近基团的分子内亲核取代对于确定反应速率很重要。这些反应的过渡态结构的变化以与分子间亲核取代类似的方式解释。通过添加微量的水，有机溶剂中的无机固体载体引起的加速变得最大。这归因于“Omega相”的形成，这是无机固体上的极性非常大的相，其中亲核试剂由于从晶格中释放且溶剂化不充分而具有活性。利用这种活性状态，通过固体碱、亲核取代和亲电加成开发了有效的催化和非催化反应。这些界面反应的选择性也可能发生改变。较少的