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Intramolecular Nitro-Aromatic Interactions Within a Molecular Torsion Balance: A Quantitative Assessment
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2018-10-18 00:00:00 , DOI: 10.1021/acs.cgd.8b01138
Brijesh Bhayana 1 , Diane A. Dickie 2
Affiliation  

Interactions between a nitro group and an aromatic ring have been identified as an important aspect within the solid-state structures of many energetic materials. We investigated nitro-aromatic interactions within a molecular “torsion balance”, both in solid-state as well as in solution. Our balance features a Tröger’s base and a nitroalkene functionality substituted at 1 and 8 positions of a naphthalene ring. Because of restricted rotation around a biaryl axis, the balance can adapt two principal atropisomeric conformations: folded and unfolded. Intramolecular nitro-aromatic interactions are feasible only in the folded state. A torsion balance containing a highly electron deficient aromatic ring crystallized in the folded state leading to the formation of a short (<3.4 Å) intramolecular NO···aromatic contact. On the other hand, with an electron rich aromatic, the balance crystallized in the unfolded conformation in which the nitro group avoids the aromatic surface. In solution, the strength of the interactions was determined to be <1 kcal/mol in different solvents. A substituent effect study showed that the interactions included a component of the electrostatic forces.

中文翻译:

分子扭转平衡内的分子内硝基芳香相互作用:定量评估。

硝基和芳环之间的相互作用已被确定为许多高能材料的固态结构内的重要方面。我们研究了固态和溶液状态下分子“扭转平衡”内的硝基-芳族相互作用。我们的天平具有Tröger碱和在萘环的1和8位取代的硝基烯烃官能团。由于绕联芳基轴的旋转受到限制,所以该天平可以适应两个主要的阻转异构构象:折叠展开。分子内硝基-芳族相互作用仅在折叠状态下才可行。包含高度电子不足的芳环的扭转平衡在折叠状态下结晶,导致形成短的(<3.4Å)分子内NO···芳族接触。另一方面,对于富电子芳族化合物,平衡基团以未折叠构象结晶,其中硝基避开了芳族化合物表面。在溶液中,在不同溶剂中相互作用的强度确定为<1 kcal / mol。取代基效应研究表明,相互作用包括静电力的一部分。
更新日期:2018-10-18
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