Carson Bradley E, Parker Trent M, Hohenstein Edward G, Brizius Glen L, Komorner Whitney, King Rollin A, Collard David M, Sherrill C David
School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr., Atlanta, GA 30332-0400 (USA), Fax: (+1) 404-894-7452.
Center for Computational Molecular Science and Technology, Georgia Institute of Technology, 901 Atlantic Dr., Atlanta, GA 30332-0400 (USA).
Chemistry. 2015 Dec 21;21(52):19168-75. doi: 10.1002/chem.201502363. Epub 2015 Nov 16.
The structural and electronic consequences of π-π and C-H/π interactions in two alkoxy-substituted 1,8-bis- ((propyloxyphenyl)ethynyl)naphthalenes are explored by using X-ray crystallography and electronic structure computations. The crystal structure of analogue 4, bearing an alkoxy side chain in the 4-position of each of the phenyl rings, adopts a π-stacked geometry, whereas analogue 8, bearing alkoxy groups at both the 2- and the 5-positions of each ring, has a geometry in which the rings are splayed away from a π-stacked arrangement. Symmetry-adapted perturbation theory analysis was performed on the two analogues to evaluate the interactions between the phenylethynyl arms in each molecule in terms of electrostatic, steric, polarization, and London dispersion components. The computations support the expectation that the π-stacked geometry of the alkoxyphenyl units in 4 is simply a consequence of maximizing π-π interactions. However, the splayed geometry of 8 results from a more subtle competition between different noncovalent interactions: this geometry provides a favorable anti-alignment of C-O bond dipoles, and two C-H/π interactions in which hydrogen atoms of the alkyl side chains interact favorably with the π electrons of the other phenyl ring. These favorable interactions overcome competing π-π interactions to give rise to a geometry in which the phenylethynyl substituents are in an offset, unstacked arrangement.
通过X射线晶体学和电子结构计算，研究了两种烷氧基取代的1,8 - 双（（丙氧基苯基）乙炔基）萘中π-π和C-H/π相互作用的结构和电子效应。类似物4的晶体结构中，每个苯环的4位带有一个烷氧基侧链，呈现出π堆积几何结构；而类似物8的每个环的2位和5位都带有烷氧基，其几何结构中各环从π堆积排列向外展开。对这两种类似物进行了对称适配微扰理论分析，以从静电、空间、极化和伦敦色散分量等方面评估每个分子中苯乙炔基臂之间的相互作用。计算结果支持了这样的预期：类似物4中烷氧基苯基单元的π堆积几何结构仅仅是最大化π-π相互作用的结果。然而，类似物8的展开几何结构是由不同非共价相互作用之间更微妙的竞争导致的：这种几何结构使得C-O键偶极呈现出有利的反排列，并且存在两个C-H/π相互作用，其中烷基侧链的氢原子与另一个苯环的π电子发生有利的相互作用。这些有利的相互作用克服了相互竞争的π-π相互作用，从而产生了一种几何结构，其中苯乙炔基取代基处于错位、未堆积的排列状态。
