Experimental and Theoretical Study of Aromatic-Aromatic Interactions. Association Enthalpies and Central and Distributed Multipole Electric Moments Analysis
Experimental and Theoretical Study of Aromatic-Aromatic Interactions. Association Enthalpies and Central and Distributed Multipole Electric Moments Analysis
复制标题
芳香-芳香相互作用的实验和理论研究。
DOI：
10.1021/jp0225828
复制
发表时间：
2003
影响因子：
3.3
通讯作者：
M. Costas
中科院分区：
文献类型：
--
作者：
Silvia Pérez;Jesús Hernández‐Trujillo;M. Costas
芳香族-芳香族相互作用的实验研究，通过热容量的测量，与援助的关联模型，提供了一个估计的关联焓的芳香族-芳香族络合物在溶液中形成的。根据经验，这些四极矩与所涉及的分子的四极矩的乘积相关。在这项工作中使用的化合物是六氟苯（HFB），五氟苯（PFB），三氟苯（TFB），氟苯，（FB），苯（BEN），甲苯（TOL），萘（NAP），和1-甲基萘（MEN）。研究的10对是HFB-MEN、HFB-BEN、HFB-TOL、NAP-HFB、PFB-MEN、PFB-BEN、HFB-FB、BEN-MEN、FB-MEN和TFB-MEN。计算了形成10个芳香-芳香对的分子之间的静电相互作用，用中心和分布多极电矩表示它们的电荷分布。结果表明，芳香-芳香复合物缔合能力的变化可以用静电作用对相互作用能的贡献来解释。I.芳香族-芳香族相互作用已被证明在化学、生物化学和材料科学中的许多系统的性质中起重要作用。[1]因此，它们在实验和理论层面上都是许多报告的主题。通常，这些相互作用发生在复杂分子的部分之间，如在许多主客体系统2和蛋白质的情况下，其中芳香族-芳香族相互作用被认为在其三级结构的稳定中是重要的。[3]在这类体系中，很难将芳香族-芳香族相互作用所起的作用与许多其他存在的作用分开，因此，研究简单的混合物是有用的。正是在这种情况下，在目前的工作中，我们研究，在实验和理论水平上，一系列的混合物中存在的芳香族分子之间的相互作用。在实验水平上，对由芳烃和芳族氟碳化合物组成的二元混合物的固-液相平衡测量表明，在固态下存在1：1的络合物。这些络合物在比纯组分高得多的温度下熔化，在六氟苯与苯4混合的情况下为19°，在六氟苯与1-甲基萘混合的情况下为约100°。[5]其他二元混合物的固液相图，如六氟苯与甲苯、对二甲苯和均三甲苯的混合物，也显示出类似的行为。六氟苯-苯配合物是迄今为止研究最多的一种配合物，已用X射线衍射、D和13 C NMR进行了表征。7得出的结论是，晶体结构由面对面堆积的分子对组成，两个分子之间的相互作用相对较弱。该复合物也已研究使用光学外差探测拉曼诱导克尔效应光谱。8在液态下，这些络合物的存在很久以前就根据热力学数据9提出，该热力学数据9表明，对于这些芳族氟碳化合物+芳烃混合物，过量吉布斯自由能G E和过量焓H E是负的，并且过量热容Cp E
Aromatic-aromatic interactions are studied experimentally through heat capacity measurements that, with the aid of an association model, provide an estimate of the association enthalpy of the aromatic -aromatic complexes formed in solution. These enthalpies are empirically correlated with the product of the quadrupole moments of the molecules involved. The compounds used in this work are hexafluorobenzene (HFB), pentafluorobenzene (PFB), triflourobenzene (TFB), flourobenzene, (FB), benzene (BEN), toluene (TOL), naphthalene (NAP), and 1-methylnaphthalene (MEN). The 10 pairs studied are HFB-MEN, HFB-BEN, HFB-TOL, NAP-HFB, PFB-MEN, PFB-BEN, HFB-FB, BEN-MEN, FB-MEN, and TFB-MEN. The electrostatic interaction between the molecules forming the 10 aromatic -aromatic pairs is calculated expressing their charge distributions in terms of both central and distributed multipole electric moments. It is concluded that the changes in association enthalpies of aromatic -aromatic complexes can be explained by the electrostatic contribution to the interaction energy. I. Introduction Aromatic-aromatic interactions have been shown to play an important role in the properties of many systems in chemistry, biochemistry, and material science. 1 For this reason, they have been the subject of numerous reports at both the experimental and theoretical levels. Often, these interactions occur between parts of complicated molecules as in the cases of many hostguest systems 2 and proteins, where aromatic-aromatic interactions have been suggested to be important in the stabilization of their tertiary structure. 3 In these kinds of systems, it is difficult to isolate the role played by the aromatic-aromatic interactions from the many others present, and hence, it is useful to examine simple mixtures. It is in this context that in the present work we study, at the experimental and theoretical levels, a series of mixtures where interactions between aromatic molecules are present. At the experimental level, solid-liquid phase equilibria measurements for binary mixtures composed of an aromatic hydrocarbon and an aromatic fluorocarbon have shown the existence of 1:1 complexes in the solid state. These complexes melt at a considerable higher temperature than the pure components, e.g., 19° in the case of hexafluorobenzene mixed with benzene 4 and approximately 100° in the case of hexafluorobenzene mixed with 1-methylnaphthalene. 5 The solidliquid phase diagrams for other binary mixtures 6 such as hexafluorobenzene mixed with toluene, with p-xylene, and with mesitylene display a similar behavior. The hexafluorobenzenebenzene complex, by far the most studied one, has been characterized by X-ray difraction and D and 13 C NMR. 7 It was concluded that the crystal structure consists of molecular pairs packed in a face-to-face manner and that the interaction between the two molecules is of a relatively weak nature. This complex has also been studied using optical heterodyne-detected Ramaninduced Kerr effect spectroscopy. 8 In the liquid state, the existence of these complexes was suggested long ago on the basis of thermodynamic data 9 which indicated that for these aromatic fluorocarbon + aromatic hydrocarbon mixtures the excess Gibbs energies G E and the excess enthalpies H E are negative and the excess heat capacities Cp E