Conformational analysis of trans-1,2-dibromocyclohexane by low-temperature cyclic voltammetry
Conformational analysis of trans-1,2-dibromocyclohexane by low-temperature cyclic voltammetry
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低温循环伏安法分析反式1,2-二溴环己烷的构象
DOI：
10.1021/ja00497a055
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发表时间：
1979
影响因子：
15
通讯作者：
Dennis H. Evans
中科院分区：
文献类型：
--
作者：
A. J. Klein;Dennis H. Evans
先生：分子的不同构象应该表现出不同的电化学行为。在足够低的温度下，用循环伏安法（CV）研究某些环四烷基肼的两种主要构象的氧化峰，以防止在实验时间尺度上的构象相互转化。我们现在报告了电化学还原的第一个例子，它显示了两个相互转换的构象中的每一个单独的CV峰值。解决方案的?拔腿就跑。2-二溴环己烷(1)有两种构象，轴向-轴向（laa）和赤道-赤道（lee）的溴间扭式构象。构象平衡高度依赖于溶剂，laa在非极性溶剂中更受青睐，而在适合电化学研究的极性溶剂中，laa和lee的分布大致相等。一项早期的核磁共振研究表明，在可达到的低温下，存在一个环反转的屏障（见表1），其高度足以“冻结”CV时间尺度上的构象相互转换。此外，参考对刚性环1,2 -二溴化物的电化学还原的研究表明，laa应该在正极电位的十分之一伏特处从lee的还原中还原。室温下，铂电极和玻碳电极分别在含0.10 M过氯酸四乙基铵的二甲基甲酰胺和含0.10 M过氯酸四乙基铵的正丁腈中观察到单还原峰。这个峰是由于快速相互转化的laa和lee的完全不可逆的双电子还原（通过库仑法证实）产生溴离子和环己烯。没有证据表明
Sir: Different conformations of a molecule should exhibit dif-ferent electrochemical behavior. It has been shown that certain cyclic tetraalkylhydrazines give separate oxidation peaks for each of their two principal conformations when studied by cyclic voltammetry (CV) at temperatures sufficiently low to prevent conformational interconversion on the time scale of the experiment. 1 We now report the first example of an elec-trochemical reduction which shows a separate CV peak for each of two interconverting conformers. Solutions of? ran. yl, 2-dibromocyclohexane (1) contain two conformers, axial-axial (laa) with the bromines anti and equatorial-equatorial (lee) with the bromines gauche. The conformational equilibrium is highly solvent dependent with laa being favored in nonpolar solvents and roughly equal populations of laa and lee presentin polar solvents suitable for electrochemical studies. 2 An early NMR study3 indicated a barrier to ring inversion (see Table I) which is high enough to “freeze out” conformational interconversion on the CV time scale at accessible low temperatures. Also, referenceto studies of the electrochemical reduction of rigid cyclic 1, 2-dibromides4 suggests that laa should be reduced at a potential several tenths of a volt positive from the reduction of lee. At room temperature on Pt or glassy carbon electrodes in dimethylformamide with 0.10 M tetraethylammonium per-chlorate or n-butyronitrile with 0.10 M tetrabutylammonium perchlorate, a single reduction peak is observed by CV. This peak is due to the totally irreversible, two-electron (confirmed by coulometry) reduction of rapidly interconverting laa and lee producing bromide ions and cyclohexene. No evidence of