STRUCTURE OF HEXAPHENYLETHANE AND CONGENERS AS DETERMINED BY EMPIRICAL FORCE-FIELD CALCULATIONS
STRUCTURE OF HEXAPHENYLETHANE AND CONGENERS AS DETERMINED BY EMPIRICAL FORCE-FIELD CALCULATIONS
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DOI：
10.1021/ja00448a038
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发表时间：
1977-01-01
影响因子：
15
通讯作者：
MISLOW, K
中科院分区：
文献类型：
--
作者：
HOUNSHELL, WD;DOUGHERTY, DA;MISLOW, K
用全弛豫经验力场计算方法计算了六苯乙烷(HPE)的结构。在势超曲面上发现了三个极小值，分别对应于具有j03、sf和du对称性的结构。计算结果表明，Z)_3基态比后者分别稳定2.55千卡/摩尔和约44千卡/摩尔。D‘基态结构由两个同手性的三丁基推进器组成，而SF形式由异手性的推进器组成，完全交错。这两种构象分子都遭受了严重的前向应变，从CCC键角的大变形和延长的中心CC键RC(1.64α)可以看出这一点。由于忽略了非谐和可能的电子效应，Rc的计算值可能是一个下限。在这种情况下，已经计算了与HPE有关的各种聚芳烃的Rc。通过交叉和反向钳位来稳定这些结构与缩短RQ有关。对HPE同系物的研究表明，与HPE形成鲜明对比的是，六苯基二硅烷基本上是无应变的，同系物系列Ph3MMPh3中的较高成员也是如此。这个系列的一个简单的力场模型能够合理地解释应变能和构象随MM键距离的变化。自从1968年Gomberg首次研究“三苯甲基”以来，六苯基乙烷(HPE)一直是化学感兴趣的焦点。证明了通常假设为HPE的三苯甲基(三丁基)自由基的二聚体实际上具有现在众所周知的亚甲基环己二烯结构(L)。2一篇引人入胜的历史故事《The
The structure of hexaphenylethane (HPE) has been computed using full relaxation empirical force field calculations. Three minima on the potential hypersurface are found, corresponding to structures with j03, Sf, and Du symmetry. The Z) 3 ground state is calculated to be more stablethan the latter conformers by 2.55 and ca. 44 kcal/mol, respectively. The D¡ ground-state structure, composed of two homochiral trityl propellers, is virtually eclipsed, whereas the Sf form, composed of heterochiral propellers, is perfectly staggered. Both conformers suffer from severe front strain between the component trityl moieties, as evidenced by major deformations of CCC bond angles and by the lengthened central CC bond rc (1.64 Á). The calculated value of rc is likely to be a lower limit due to neglect of enharmonic and possible electronic effects. In this context, rc has been calculated for a variety of polyarylethanes relatedto HPE. Stabilization of these structures by cross and back clamping has been correlated to a shortened rQ. A study of HPE homologues has revealed that hexaphenyldisilane, in marked contrast to HPE, is essentially strain free, as are the higher members in the homologous series Ph3MMPh3. A simple force field model for this series has been devised which is capable of rationalizing changes in strain energy and conformation as a function of MM bond distance.Hexaphenylethane (HPE) has been a focal point of chem-ical interest since Gomberg’s initial investigation of “tri-phenylmethyl” in 1900.1 In 1968, it was proven that the dimer of triphenylmethyl (trityl) radicals, generally assumed to be HPE, actually has the now well-known methylenecyclohexa-diene structure (l). 2 A fascinating historical account of “The