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首页> 外文期刊>Crystal growth & design >Do 12-membered cycloalkane rings only exist as one conformation in the solid-state? A detailed solid-state analysis involving polymorphs of N,N′-biscyclododecyl pyromellitic diimide
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Do 12-membered cycloalkane rings only exist as one conformation in the solid-state? A detailed solid-state analysis involving polymorphs of N,N′-biscyclododecyl pyromellitic diimide

机译：12元环烷烃环仅以一种构象形式存在于固态中吗？详细的固态分析，涉及N，N'-双环十二烷基均苯四甲酸二酰亚胺的多晶型物

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摘要

Conformational flexibility in molecules plays a key role in many chemical and biological processes. It is a common belief that the larger the cycloalkane the more flexible it will be, and the more conformations it will adopt. While theoretical studies have shown that cyclododecane has many possible conformations, they have also consistently shown that one conformation is slightly more stable. In this work, we examine the effect of substitution and crystal packing on the conformation of singly substituted cyclododecane rings. This has been done by exploiting polymorphism in an attempt to induce new conformations in a specific molecule, as well as by examining structures reported in the Cambridge Structural Database (CSD). To this end, three polymorphs of N,N′-biscyclododecyl pyromellitic diimide (PMDI-12) have been identified and their structures elucidated. To rationalize the differences between the various polymorphs, molecule?molecule interaction energies have been calculated using atom-atom potential methods. Though the conformation of the PMDI-12 molecules as a whole may differ, examination of the conformation of the 12-membered ring indicates that it is conformationally identical in all three polymorphs. Examination of 20 other organic and organometallic structures containing this group in the CSD, indicates that they have the same conformation (only one possible exception in the 34 rings examined in this work), which suggests that the 12-membered ring adopts a single conformation ([3333] with D_2 symmetry) in the solid-state that is relatively unaffected by crystal packing.
机译：分子的构象柔韧性在许多化学和生物学过程中起着关键作用。通常认为，环烷烃越大，它越柔韧性，并且采用的构象就越多。尽管理论研究表明环十二烷具有许多可能的构象，但他们也始终如一地表明一种构象稍微更稳定。在这项工作中，我们研究了取代和晶体堆积对单取代的环十二烷环构象的影响。这是通过利用多态性试图在特定分子中诱导新构象以及通过检查剑桥结构数据库（CSD）中报道的结构来完成的。为此，已经鉴定出N，N′-双环十二烷基均苯四酸二酰亚胺（PMDI-12）的三种多晶型物，并阐明了它们的结构。为了合理化各种多晶型物之间的差异，已使用原子-原子电势方法计算了分子-分子相互作用能。尽管整个PMDI-12分子的构象可能有所不同，但检查12元环的构象表明，它在所有三个多晶型物中的构象都相同。在CSD中对包含此基团的其他20种有机和有机金属结构进行的研究表明，它们具有相同的构象（在本研究中检查的34个环中只有一个可能的例外），这表明12元环采用了一个构象（ [3333]（具有D_2对称性）处于固态，相对不受晶体堆积的影响。

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