Structure of π-π Interactions in Aromatic Liquids
Structure of π-π Interactions in Aromatic Liquids
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DOI：
10.1021/ja909084e
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发表时间：
2010-04-28
影响因子：
15
通讯作者：
Soper, Alan K.
中科院分区：
文献类型：
--
作者：
Headen, Thomas F.;Howard, Christopher A.;Soper, Alan K.
高分辨率中子衍射已被用于与氢/氘同位素标记，以确定前所未有的详细结构的两个原型芳香族液体：苯和甲苯。我们发现的芳香族π-π相互作用的性质，在液体状态下，通过构建这些系统的第一次完整的六维空间和取向的图片。我们发现，在每种情况下，最近邻配位壳层包含约12个分子。苯是两种液体中结构更好的，例如，在径向分布函数中显示出更尖锐的最近邻配位峰。从表面上看，第一邻居壳似乎各向同性，但我们的多维分析表明，在这些液体中的局部取向顺序要复杂得多。在小的分子间距（5埃），相邻的芳环主要是垂直的，每个分子有两个H原子指向受体的π轨道。所谓的“反氢键”的配置，提出作为全球最低的苯二聚体，只发生在我们的数据作为一个鞍点。因此，所观察到的液体结构是从根本上不同于那些推导出的分子二聚体能量表面。
High-resolution neutron diffraction has been used in conjunction with hydrogen/deuterium isotopic labeling to determine with unprecedented detail the structure of two archetypal aromatic liquids: benzene and toluene. We discover the nature of aromatic pi-pi interactions in the liquid state by constructing for the first time a full six-dimensional spatial and orientational picture of these systems. We find that in each case the nearest neighbor coordination shell contains approximately 12 molecules. Benzene is the more structured of the two liquids, showing, for example, a sharper nearest neighbor coordination peak in the radial distribution function. Superficially the first neighbor shells appear isotropic, but our multidimensional analysis shows that the local orientational order in these liquids is much more complex. At small molecular separations (5 angstrom) the neighboring aromatic rings are predominantly perpendicular, with two H atoms per molecule directed toward the acceptor's pi orbitals. The so-called "anti-hydrogen-bond" configuration, proposed as the global minimum for the benzene dimer, occurs only as a saddle point in our data. The observed liquid structures are therefore fundamentally different than those deduced from the molecular dimer energy surfaces.