Pareras Gerard, Szczepanik Dariusz W, Duran Miquel, Solà Miquel, Simon Sílvia
School of Chemistry , University College Cork , College Road , Cork T12 K8AF , Ireland.
Institut de Química Computacional i Catàlisi and Departament de Química , Universitat de Girona , C/ Maria Aurèlia Capmany 69 , 17003 Girona , Catalonia , Spain.
J Org Chem. 2019 Dec 6;84(23):15538-15548. doi: 10.1021/acs.joc.9b02526. Epub 2019 Nov 21.
The fact that intramolecular resonance-assisted hydrogen bonds (RAHBs) are stronger than conventional ones is attributed to the partial delocalization of the π-electrons within the hydrogen bond (HB) motif, the so-called quasi-ring. If an aromatic ring is involved in the formation of the RAHB, previous studies have shown that there is an interplay between aromaticity and HB strength. Moreover, in 1,3-dihydroxyaryl-2-aldehydes, some of us found that the position of the quasi-ring formed by the substituents interacting through RAHB influences the strength of the H bonding, the HBs being stronger when a kinked-like structure is generated by formation of the quasi-ring. In this work, we explore this concept further by considering a set of acenes and phenacenes of different sizes with two hydroxyaldehyde substituents. Calculations with the CAM-B3LYP/6-311++G(d,p) + GD3B method show that for long acenes or phenacenes, once the substituent effect loses importance because quasi-rings are pulled apart far from each other, the different topologies rule the HB distances. This fact can be explained in most cases using an extended Clar's aromatic π-sextet model. In some kinked systems, however, the justification from the Clar model has to be complemented by taking into account the repulsion between hydrogen atoms. Triphenylene-like compounds with different numbers of benzene rings have been studied, finding out a very good relationship between aromaticity of the ipso- and quasi-rings with the RAHB distances. This result confirms the importance of the communication of the π-systems of the ipso- and quasi-rings.
分子内共振辅助氢键（RAHBs）比传统氢键更强这一事实，归因于氢键（HB）基序（即所谓的准环）内π电子的部分离域。如果一个芳环参与RAHB的形成，先前的研究表明芳香性和HB强度之间存在相互作用。此外，在1,3 - 二羟基芳基 - 2 - 醛中，我们中的一些人发现通过RAHB相互作用的取代基形成的准环的位置会影响氢键的强度，当通过形成准环产生扭结状结构时，氢键更强。在这项工作中，我们通过考虑一组具有两个羟基醛取代基的不同尺寸的并苯和菲来进一步探索这一概念。使用CAM - B3LYP/6 - 311++G(d,p) + GD3B方法进行的计算表明，对于长并苯或菲，一旦由于准环彼此拉开距离而使取代基效应变得不重要，不同的拓扑结构就会决定HB距离。在大多数情况下，这一事实可以用扩展的克拉尔芳香π - 六隅体模型来解释。然而，在一些扭结系统中，必须考虑氢原子之间的排斥力来补充克拉尔模型的解释。已经研究了具有不同苯环数目的类三亚苯化合物，发现原位环和准环的芳香性与RAHB距离之间存在非常好的关系。这一结果证实了原位环和准环的π系统通信的重要性。
