Investigation of steric influences on hydrogen-bonding motifs in cyclic ureas by using X-ray, neutron, and computational methods.
Investigation of steric influences on hydrogen-bonding motifs in cyclic ureas by using X-ray, neutron, and computational methods.
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使用 X 射线、中子和计算方法研究环状脲中氢键基序的空间影响。
DOI：
10.1002/asia.201300530
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
D. Turner
中科院分区：
文献类型：
--
作者：
Laura J. McCormick;C. McDonnell;J. Platts;A. Edwards;D. Turner
制备了一系列脲衍生杂环化合物，即5N-取代的六氢-1,3,5-三嗪-2-酮，并首次确定了它们的结构。该族化合物仅在 5 位取代基（衍生自相应的伯胺）上有所不同，即甲基 (1)、乙基 (2)、异丙基 (3)、叔丁基 (4)、苄基 (5)、N,N-(二乙基)乙胺 (6) 和 2-羟乙基 (7)。这些分子的共同杂环核心是环状脲，它有可能形成由自缔合的 R22(8) 二聚体组成的氢键带基序。 X 射线晶体学和（如果可能）劳厄中子晶体学的结果表明，观察到的氢键基序和氢键的平面性似乎取决于 N 取代基的 α-碳原子处的空间位阻。对于受阻较少的取代基甲基和乙基，观察到了预期的带基序。当在 α-碳原子上添加额外的甲基时（如异丙基和叔丁基衍生物），会观察到不同的 2D 氢键基序。尽管取代基庞大，但苄基和 N,N-(二乙基)乙胺衍生物在 α-碳原子处具有亚甲基单元，因此显示出带基序。在 2-羟乙基衍生物中引入竞争性氢键供体/受体会破坏带基序，羟基会中断 N-H…O=C 相互作用。化合物 2 和 5 的含氢氮原子周围的几何形状（无论是平面还是非平面）已通过劳厄中子衍射得到证实，并通过计算方法合理化，从而证明 O-C-N-H 扭转角的扭曲发生以维持几乎线性的氢键相互作用。
A series of urea-derived heterocycles, 5N-substituted hexahydro-1,3,5-triazin-2-ones, has been prepared and their structures have been determined for the first time. This family of compounds only differ in their substituent at the 5-position (which is derived from the corresponding primary amine), that is, methyl (1), ethyl (2), isopropyl (3), tert-butyl (4), benzyl (5), N,N-(diethyl)ethylamine (6), and 2-hydroxyethyl (7). The common heterocyclic core of these molecules is a cyclic urea, which has the potential to form a hydrogen-bonding tape motif that consists of self-associative R₂²(8) dimers. The results from X-ray crystallography and, where possible, Laue neutron crystallography show that the hydrogen-bonding motifs that are observed and the planarity of the hydrogen bonds appear to depend on the steric hindrance at the α-carbon atom of the N substituent. With the less-hindered substituents, methyl and ethyl, the anticipated tape motif is observed. When additional methyl groups are added onto the α-carbon atom, as in the isopropyl and tert-butyl derivatives, a different 2D hydrogen-bonding motif is observed. Despite the bulkiness of the substituents, the benzyl and N,N-(diethyl)ethylamine derivatives have methylene units at the α-carbon atom and, therefore, display the tape motif. The introduction of a competing hydrogen-bond donor/acceptor in the 2-hydroxyethyl derivative disrupts the tape motif, with a hydroxy group interrupting the N-H···O=C interactions. The geometry around the hydrogen-bearing nitrogen atoms, whether planar or non-planar, has been confirmed for compounds 2 and 5 by using Laue neutron diffraction and rationalized by using computational methods, thus demonstrating that distortion of O-C-N-H torsion angles occurs to maintain almost-linear hydrogen-bonding interactions.
影响因子：
2.5
作者：
McPhillips, TM;McPhillips, SE;Kuhn, P
通讯作者：
Kuhn, P