Electronic spectra and molecular structure of biphenyl and para-substituted biphenyls in a supersonic jet
Electronic spectra and molecular structure of biphenyl and para-substituted biphenyls in a supersonic jet
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超音速射流中联苯和对位取代联苯的电子光谱和分子结构
DOI：
10.1021/j100314a003
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
K. Kaya
中科院分区：
文献类型：
--
作者：
Yuichiro Takei;Taro Yamaguchi;Y. Osamura;K. Fuke;K. Kaya
作为结构有机化学和物理化学的基本问题，联苯的分子结构一直是两个苯环之间扭转角众多研究的主题。111虽然在常温下处于结晶状态的联苯的分子结构已知是平面的，但是2晶体在低温条件下经历相变而具有非平面结构。3 - 9溶液中的几项光学研究表明，联苯具有约15-30扭曲的结构从平面几何形状。对气态联苯的电子衍射研究得出结论，扭转角约为45 °。16，17联苯的扭曲结构可以通过两个苯环邻位的氢-氢排斥和电子离域效应之间的平衡来解释。前者的不稳定化使两个芳环垂直，而后者的稳定化倾向于保持红外电子在同一平面。这两种相互对立的效应微妙地保持着平衡，以至于二面角可能会随着环境（气相、液相或固相）的变化而呈现出实质性的变化。从头计算预测的扭转运动的势垒高度相对较小，约。2-2.5千卡/摩尔。18
The molecular structure of biphenyl has been the subject of numerous investigations on the torsional angle between two phenyl rings, as a basic problem of structural organic and physical chemistry. 1 11While the molecular structure of biphenyl in the crystalline state at ordinary temperature is known to be planar, 2 the crystal undergoes phase transition to have a nonplanar structure in the low-temperature condition. 3" 9 The several optical studies in solution suggest that biphenyl has ca. 15-30 twisted structure from the planar geometry. 10" 15 The electron diffraction studies on the gaseous biphenyl conclude that the torsional angle is about 45. 16, 17 The twisted structure of biphenyl has been explained by the balance between the hydrogen-hydrogen repulsion in the ortho position of two phenyl rings and the electron delocalization effect. The former destabilization brings two aromatic rings perpendicular, while the latter stabilization tends to keep the ir-electrons in the same plane. These two opposing effects keep balance with each other so subtly that the dihedral angle might exhibit sub-stantial variation with the change of the environment (gas, liquid, or solid phase). The ab initio calculationpredicts relatively small barrier height of torsional motion, ca. 2-2.5 kcal/mol. 18