Mechanism of base-catalysed hydrogen–deuterium exchange in thiazolium ion: evidence for the involvement of a tetrahedral intermediate
作者:Khashayar Karimian、Fatemeh Mohtarami、Massoud Askari
DOI:10.1039/p29810001538
日期:——
slow exchange of 2-H in (1), (3), and (4), concomitant with H–D exchange of the 4- and 5-methyl protons. The rate of exchange of (1) is found to be approximately twice as rapid as that of (3) or (4). No H–D exchange of 2-H is detected in the case of (2) with the hindered nucleophile. These observations are ascribed to the formation of a tetrahedral intermediate as a prerequisite of the exchange reaction
噻唑鎓离子中2-H的碱催化氢-氘交换的机理已通过1 H nmr光谱法进行了研究,使用的是空间受限的亲核小分子。在3,4,5-三甲基-(1),3-甲基-4,5-二苯基-(2),3,5-的情况下,在[ 2 H 6 ] Me 2 SO中观察到快速的H-D交换当小的亲核试剂(KOD–D 2 O或KOCD 3 –DOCD 3; 0.016 M; 25°)存在时,二甲基-4-苯基-(3)和3,4-二甲基-5-苯基-噻唑碘化物(4)受雇。利用受阻亲核试剂[KOC(CD 3)3 –DOC(CD 3)3 ; 0.016中号; [25°]导致(1),(3)和(4)中2-H的缓慢交换,同时伴随着4-和5-甲基质子的H-D交换。发现(1)的交换速率大约是(3)或(4)的交换速率的两倍。在(2)中,受阻亲核试剂未检测到2-H的H-D交换。这些观察结果归因于四面体中间体的形成作为交换反应的先决条件。