SULFURANCES - THEORETICAL ASPECTS OF BONDING, SUBSTITUENT SITE PREFERENCES, AND GEOMETRICAL DISTORTIONS
SULFURANCES - THEORETICAL ASPECTS OF BONDING, SUBSTITUENT SITE PREFERENCES, AND GEOMETRICAL DISTORTIONS
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DOI：
10.1021/ja00423a001
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发表时间：
1976-01-01
影响因子：
15
通讯作者：
HOFFMANN, R
中科院分区：
文献类型：
--
作者：
CHEN, MML;HOFFMANN, R
对硫烷SR_4电子结构的分子轨道分析发现，它与磷烷有许多相似之处。基本的图像是富电子的三中心键，伴随着削弱轴向债券和富电子轴向网站。硫烷的新特征是在赤道平面上具有方向性孤对电子，这一点在确定带有x-型电子的取代基的构象优先性方面尤其明显。三中心键的非键轨道与S孤对轨道具有相同的对称性。它们混合并竞争作为分子的最高占据分子轨道的位置。SR 4结构的取代基位置偏好与正膦的效应相同，即更多的电负性取代基应进入轴向位置。对于x效应，通过硫孤对的存在来修改偏好。关于轴向取代和赤道键角的相互关系，得出了几个结论：（1）轴向和赤道键强度的差异应随赤道角的增加而减小;（2）如果轴向键被拉伸，人们预期赤道角将减小;（3）在轴向位置被更多的电负性配体取代，应有利于赤道配体之间的较小角度。支持这些结论是寻求在各种S，Se，andTe结构。
A molecular orbital analysis of the electronicstructure of sulfuranes, SR4, finds many analogies to the phospho-ranes. The basic picture is of electron-rich three-center bonding, with concomitant weakened axial bonds and electron-rich axial sites. The novelfeature of the sulfuranes is a directional lone pair in the equatorial plane, whichmakes itself felt espe-cially in setting conformational preferences for substituents bearing x-type electrons. The nonbonding orbital of the three-center bond andthe S lone pair are of the same symmetry type. They mix and compete for position as the highest occupied molecular orbital of the molecule. Substituent site preferences for the SR4 structure are the same as for thephosphoranes for effects, ie, more electronegative substituents should enter the axial sites. For x effects the preferences are modified by the presence of the sulfur lone pair. Several conclusions are drawn concerning the interrelationship of axial substitution and the equatorial bondangle:(1) the difference in axial and equatorial bond strengths should lessen with increasing equatorial angle;(2) if the axial bonds are stretched, one expects the equatorial angleto decrease;(3) substitution in the axial positions by more electronegative ligands should favor a smaller angle between the equatorial ligands. Support for these conclusions is sought in assorted S, Se, andTe structures.