Thermal rearrangement of α,β- to β,γ-unsaturated esters. Evidence for a 1,5-hydrogen transfer mechanism
作者:Donald E. McGreer、Norman W. K. Chiu
DOI:10.1139/v68-362
日期:1968.7.1
found to rearrange at 252 °C by a simple first-order and presumably unimolecular mechanism to methyl 4-methyl-3-pentenoate (3) with a rate constant k of 4.28 × 10−5 s−1. The heat of activation ΔH†, was determined to be 37.5 ± 2 kcal/mole and the entropy of activation, ΔS†, was determined to be −8.2 ± 4 e.u. These activation parameters and the steric requirements of the reaction support a mechanism involving
已发现顺式-4-甲基-2-戊烯酸甲酯 (1) 在 252 °C 通过简单的一级和推测的单分子机制重排为 4-甲基-3-戊烯酸甲酯 (3),速率常数 k 为4.28 × 10−5 s−1。活化热 ΔH† 确定为 37.5 ± 2 kcal/mol,活化熵 ΔS† 确定为 -8.2 ± 4 eu 这些活化参数和反应的空间要求支持涉及氢的循环 1,5-转移。对顺式-2-戊烯酸甲酯、顺式-2,4-二甲基-2-戊烯酸甲酯和顺式-2-甲基-2-戊烯酸甲酯异构化为相应的 3-戊烯酸酯的研究表明,1,5-氢转移机制对于 α,β- 和 β,γ-不饱和酯的平衡很可能是通用的。核磁共振显示,双键上与甲基或碳甲氧基顺式的异丙基优选具有远离甲基或碳甲氧基的异丙基甲基的构象。一个...