PHOTOELECTRON-SPECTRA OF ALKYL ARYL SELENIDES - ELECTRONIC AND STERIC FACTORS IN THE OBSERVATION OF ROTAMERS
PHOTOELECTRON-SPECTRA OF ALKYL ARYL SELENIDES - ELECTRONIC AND STERIC FACTORS IN THE OBSERVATION OF ROTAMERS
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DOI：
10.1021/jo00334a003
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发表时间：
1981-01-01
影响因子：
3.6
通讯作者：
GROSSMAN, J
中科院分区：
文献类型：
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作者：
BAKER, AD;ARMEN, GH;GROSSMAN, J
测量了几种芳基烷基硒醚的光电子能谱。几个光谱显示存在两种主要的旋转异构体的证据，一种具有最大重叠，一种具有最小重叠。利用本文建立的相互作用模型，我们揭示了空间因素如何影响旋转异构体的分布，并证明了电子效应决定了不同的旋转异构体能否被光电子技术检测到，苯衍生物的光电子能谱提供了有关这些物种中电子效应和空间效应的丰富信息。对于分子，如苯酚，苯基醚，苯胺，低电离电位（IP）区域的光谱很容易分配134通过参考分子轨道能级图，其中一个已allowedp轨道上的取代基与苯Bt轨道相互作用。在这种情况下的默认假设是，只需要考虑平面或近似平面的构象，其中取代基p轨道的取向与苯基Bx轨道的重叠最大。这种化合物的光电子能谱的低IP区缺乏复杂性，这通常支持这种假设，因为远离平面形式的旋转异构形式的存在将导致观察到额外的光电子带或比实际观察到的带明显更宽。然而，也可以预期，大的取代基可能会改变这一情况。事实上，叔丁基苯基醚3，4和其他具有大邻位取代基的化合物5的光电子能谱确实反映了这些分子的空间约束。一个特别有趣的情况出现与苯基硫族化物，因为无论是理论6 7和实验研究，包括光电子研究，8，9表明，在某些情况下，可能有一个相当接近的能量平衡之间的两个极端的旋转异构形式，指定为平面（I）和perpdicular（）。早期的计算表明，
The photoelectron spectra of several aryl alkyl selenides have been measured. Several of the spectra show evidence for theexistence of two predominant rotamers, one with maximum-overlap and one with minimal overlap. Using the interaction model developed here, we show how steric factorseffect rotamer populations and demonstrate that electronic effects determine whether or not different rotamers can bedetected by the photoelectron technique.The photoelectron spectra of benzene derivatives have provided copious information about electronic and steric effects in these species. For molecules such as phenols, phenyl ethers, and anilines, the low ionization potential (IP) region of the spectrum is readily assigned1 34by reference to a molecular orbital energy level diagram in which one has allowedthe p orbital on the substituent to interact with the benzene Bt orbital. The tacit assumption in such cases is that it is necessary only to consider a planar or nearly planar conformation in which the substituent p orbital is oriented for maximum overlap with the phenyl Bx orbital. Lack of complexity in the low-IP regions of the photo-electron spectra of such compoundsgenerally support this assumption, since the presence of rotameric forms far re-moved from the planar form would result in either the observation of additionalphotoelectron bands or in bands appreciably broader than those actually observed. Nevertheless, it is also to be expected that large substituent groups could alter this picture. Indeed, the photoelectron spectra of terf-butyl phenyl ether3, 4 and of other com-pounds with large ortho substituents5do reflect the steric constraints placed on these molecules. A particularly interesting situation arises with phenyl chalcogenides, since both theoretical6 7and experimental studies, including photoelectron studies, 8, 9 suggest that in some cases there may be a fairly close balance in energy between two extreme rotameric forms, designated as planar (I) and perpdicular (). Earlier calculations6 had suggested