Electrophilic aromatic reactivities via pyrolysis of esters. Part 21. σ<sup>+</sup>Values for thiazole: the high polarisability of thiazole, and the effect of hydrogen bonding on the reactivity of N-containing heterocycles
作者:Ryan August、Carole Davis、Roger Taylor
DOI:10.1039/p29860001265
日期:——
values 0.93, 0.505, and –0.07. The positional reactivity order, and the reactivity relative to benzene, are correctly predicted by π-electron density calcuations. The reactivity of each position is substantially less than in solvolysis of the corresponding 1-aryl-1-chloroethanes, in contrast to the reactivity of thiophene which is closely similar in both pyrolysis and solvolysis reactions. Thiazole is thus
在633.2至698.5 K之间测得了从1-芳基乙酸乙酯(气相色谱中芳基=噻唑-2-基,噻唑-4-基,噻唑-5-基或苯基)中乙酸的气相消除速率。在650K下的热解速率为:噻唑-2-基,0.271;和。噻唑-4-基,0.491; 和噻唑-5-基,1.104;和 再加上先前确定的反应ρ因子(在650 K时为–0.61),则得出相应的σ +值0.93、0.505和–0.07。通过π电子密度计算正确地预测了位置反应性顺序和相对于苯的反应性。与噻吩的反应性在热解和溶剂分解反应中都非常相似的相反,每个位置的反应性基本上小于相应的1-芳基-1-氯乙烷的溶剂化反应。因此,噻唑比噻吩具有更大的极化性,因此特别容易受到各个过渡态共振稳定化的需求,在热解中需求较少。噻唑2位和相应的噻吩α位反应性之间的差异(1。72 sigma单位)明显大于噻唑4位和噻吩β位置(0.885 sigma单位)的反应性之差。这反映出较高的2