Mesomeric Vinyl Cations. Part II. Solvolysis of 2‐bromo‐1, 3‐butadienes
Mesomeric Vinyl Cations. Part II. Solvolysis of 2‐bromo‐1, 3‐butadienes
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介观乙烯基阳离子第二部分。
DOI：
10.1002/hlca.19700530824
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发表时间：
1970
影响因子：
1.8
通讯作者：
R. Spaar
中科院分区：
文献类型：
--
作者：
C. A. Grob;R. Spaar
与2-溴-1，3-丁二烯（5）相反，二-、三-和四甲基衍生物6-11显示出显著的溶剂分解反应性.测定了这些溴代二烯在80%乙醇中的一级反应速率常数和产物。速率对溶剂的电离能力非常敏感，但不受三乙胺的影响。生成了三种类型的产物，即烯炔、α，β-不饱和酮和4-乙氧基联烯。
5的C-4上的一个甲基使反应速率增加约1倍。102;两个甲基基团使速率增加约。104.在C-1的甲基取代基只有轻微的影响，显然是由于速率降低的极性效应和补偿速率增加的空间效应。
这项研究的结果是一致的单分子电离机制，涉及作为中间体的内消旋乙烯基阳离子12 a-12 b。
In contrast to 2-bromo-1, 3-butadiene (5), the di-, tri- and tetramethyl derivatives 6–11 show remarkable solvolytic reactivity. First order rate constants and products of these bromodienes in 80% ethanol have been determined. Rates are very sensitive to the ionising power of the solvent but are not affected by triethylamine. Three types of products are formed, i.e. alkenynes, α,β-unsaturated ketones and 4-ethoxyallenes.
One methyl group on C-4 of 5 increases the reaction rate by a factor of ca. 102; two methyl groups increase the rate by ca. 104. Methyl substituents at C-1 have only a slight influence, apparently as a result of a rate-decreasing polar effect and a compensating rate-increasing steric effect.
The results of this study are consistent with a unimolecular ionization mechanism involving a mesomeric vinyl cation 12a 12b as an intermediate.