CRITICAL EXAMINATION CONCERNING THE MECHANISTIC POSTULATES IN SOLVOLYTIC DISPLACEMENT REACTIONS

定量分析离子中间体在溶解过程中返回到起始物质的过程对研究其反应机理起着决定性的作用。利用同位素氧取代引起的烷基磺酸酯的~&lt；13&gt；C核磁共振信号中的裂解来定量确定磺酸盐部分中三个氧原子之间的~&lt；18&gt；O的竞争程度。在密封的核磁共振管中，使用少量的双标记起始对甲苯磺酸盐，成功地完成了氧交换过程(返回过程)以及整个溶剂分解过程。在新对甲苯磺酸酯的乙酰解反应中，在整个反应范围内没有检测到起始对甲苯磺酸盐的烷氧基氧上的^&lt；18&gt；O-争夺性。2-(对甲苯基)对甲苯酸乙酯经乙酰化反应得到重排的对甲苯磺酸酯，三个氧基完全随机化。2-苯丙酯和2-苯乙基对甲苯磺酸酯的乙酰化反应也得到了重排的…两个信号的更多对甲苯磺酰化，伴随着不完全的氧平衡。不同取代苯乙基对甲苯磺酸盐的不同干扰行为可能与离子对的性质有关。在对甲苯磺酸苯乙酯的乙酰解反应中，(1-^*C)-OTS^*和(2-^*C)-OTS^*的平行运行表明，在返回过程中，两个亚甲基碳相当于从磺酰基氧中引入的^&lt；18&gt；O-。这提供了强有力的证据表明，只有在形成对称的苯离子物种后，才会发生^&lt；18&gt；O的扰乱。在对甲苯磺酸苄酯的乙酰化反应中，检测到了^&lt；18&gt；O-杂乱，与S_N_2反应机理不一致。2-金刚烷基对甲苯磺酸酯的乙酰化反应也出现了离子对返回，这表明有必要重新审视溶解理论。显然，比质谱法更优越的核磁共振方法一般可用于研究溶剂分解的返回过程。较少

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