CRITICAL EXAMINATION CONCERNING THE MECHANISTIC POSTULATES IN SOLVOLYTIC DISPLACEMENT REACTIONS

定量分析溶剂分解反应中离子中间体向起始原料的返回过程对研究反应机理具有决定性作用，本文利用<13>同位素氧取代引起的烷基磺酸酯~ 1C NMR信号<16>的裂解<18>，定量测定<18>磺酸酯结构中三个氧原子间的^ O乱序程度。在氧交换过程（返回过程）以及整个溶剂分解过程之后，成功地进行了13 <13>C NMR光谱法，其在密封的NMR管中使用少量双标记的起始甲苯磺酸盐。在甲苯磺酸新叶酯的乙酰解反应中，<18>在整个反应范围内，在起始甲苯磺酸酯的烷氧基氧上根本没有检测到^O-乱序。2-（p-OMe-苯基）乙基甲苯磺酸酯的乙酰解得到重排的甲苯磺酸酯，其三个氧完全无规化。对甲苯磺酸2-苯丙基酯和2-苯乙基酯的乙酰甲苯裂解也得到了重排产物 关于我们 两个信号的甲苯磺酸盐，伴随着不完全的氧平衡。取代的苯乙基甲苯磺酸酯的不同的扰乱行为，可能是由于离子对的性质。在甲苯磺酸2-苯乙酯的乙酰解中，（1-^*C）-OTs^* 和（2-^*C）-OTs^* 的平行运行表明，<18>在返回过程中，从磺酰氧引入的^O-相当于两个亚甲基碳。这提供了强有力的证据，证明^<18>O的混乱只发生在对称的酚离子物种形成之后。在甲苯磺酸苄酯的乙酰化反应中，<18>发现了与S_N2机理不一致的^O-乱序现象，在典型k_c底物的2-金刚烷基甲苯磺酸酯的乙酰化反应中也发现了离子对返回现象，提示有必要重新审视溶剂分解理论。显然，~ 13 <13>C NMR方法上级优于质谱法，可普遍适用于溶剂分解返回过程的研究。少

Quantitative analysis of the return process from ionic intermediates to the starting material in solvolysis plays a decisive role in the investigation of its reaction mechanism.The splitting, in the ^<13>C NMR signals of alkyl sulfonate esters, induced by isotopic oxygen substitution ^<16>O/^<18>O, was utilized to determine quantitatively the extent of ^<18>O scrambling within three oxygens in the sulfonate moiety. Oxygen exchange process (return process) as well as overall solvolysis process was successfully followed by ^<13>C NMR spectroscopy using a small amount of doubly labeled starting tosylate in a sealed NMR tube. In the acetolysis of neophyl tosylate, no ^<18>O-scrambling at the alkoxy oxygen of the starting tosylate was detected at all for whole range of reaction. The acetolysis of 2-(p-OMe-phenyl)ethyl tosyate gave the rearranged tosylates with complete randomization of the three oxygens. The ace- tolyses of 2-phenylpropyl and 2-phenylethyl tosylates also gave the rearranged … More tosylates of two signals, accompanying the incomplete oxygen equilibration. The different scrambling behaviors for substituted phenylethyl tosylates, may be attributable to the nature of the ion-pairs. In the acetolysis of 2-phenylethyl tosylate, parallel runs of (1-^*C)-OTs^* and (2-^*C)-OTs^* indicated the equivalence of two methylene carbons for ^<18>O-incorporation from sulfonyl oxygens in the return process. This provides strong evidence that the ^<18>O scrambling occurs only after the formation of symmetrical phenonium-ion species. In the acetolysis of benzyl tosylate, ^<18>O-scrambling was detected, being inconsistent with S_N2 mechanism.The acetolysis of 2-adamantyl tosylate referred to a typical k_c substrate also showed the occurrence of ion-pair return, suggesting the necessity of re-examination of solvolysis theories. It is apparent that the ^<13>C NMR method superior to the mass spectroscopic method can generally be applicable to the investigation of the return process in solvolysis. Less