Structural and thermodynamic characterization of polyphenylbenzenes.
Structural and thermodynamic characterization of polyphenylbenzenes.
复制标题
聚苯的结构和热力学表征。
DOI：
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发表时间：
2011
影响因子：
2.9
通讯作者：
Luís M. N. B. F. Santos
中科院分区：
文献类型：
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作者：
C. Lima;M. A. Rocha;A. Melo;L. Gomes;J. N. Low;Luís M. N. B. F. Santos
本文研究了从n(Ph)=0到六苯(n(Ph)=6)的一系列多苯基苯的热力学和结构。通过测定1，2，4-三苯基苯、1，2，4，5-四苯基苯和六苯基苯的相关热力学性质，以及通过X射线结晶学对一些所研究的化合物进行结构测定，扩展了这类化合物的现有文献数据。这类化合物中的气相能量是从气相中的标准摩尔生成热来分析的。通过量子化学计算，得到了某些多苯基苯中苯基苯基受阻转动的扭转分布，以及气相结构和能量学。在理想气相中，由于六个苯基之间的空间拥挤，六苯基苯相对于其他多苯基苯表现出明显的热失稳现象。观察到六苯基苯的升华热相对较低，这与能够建立分子间相互作用的减小的表面积一致。观察到六苯基苯的明显反常的低升华熵是由其高分子对称性和六个高度受阻的苯环内旋所解释的。对于所考虑的系列多苯基苯，升华熵的差异主要归因于气相中苯基取代基的扭转自由度和与分子对称性有关的熵项。
The thermodynamic and structural study of a series of polyphenylbenzenes, from benzene, n(Ph) = 0, to hexaphenylbenzene, n(Ph) = 6, is presented. The available literature data for this group of compounds was extended by the determination of the relevant thermodynamic properties for 1,2,4-triphenylbenzene, 1,2,4,5-tetraphenylbenzene, and hexaphenylbenzene, as well as structural determination by X-ray crystallography for some of the studied compounds. Gas phase energetics in this class of compounds was analyzed from the derived standard molar enthalpies of formation in the gaseous phase. The torsional profiles relative to the phenyl-phenyl hindered rotations in some selected polyphenylbenzenes, as well as the gas phase structures and energetics, were derived from quantum chemical calculations. In the ideal gas phase, a significant enthalpic destabilization was observed in hexaphenylbenzene relative to the other polyphenylbenzenes, due to steric crowding between the six phenyl substituents. A relatively low enthalpy of sublimation was observed for hexaphenylbenzene, in agreement with the decreased surface area able to establish intermolecular interactions. The apparently anomalous low entropy of sublimation observed for hexaphenylbenzene is explained by its high molecular symmetry and the six highly hindered phenyl internal rotations. For the series of polyphenylbenzenes considered, it was shown that the differentiation in the entropy of sublimation can be chiefly ascribed to the torsional freedom of the phenyl substituents in the gas phase and the entropy terms related with molecular symmetry.