An eclipsed C(sp3)−CH3 bond in a crystalline hydrated tricyclic orthoamide: evidence for C−H••••O hydrogen bonds
An eclipsed C(sp3)−CH3 bond in a crystalline hydrated tricyclic orthoamide: evidence for C−H••••O hydrogen bonds
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结晶水合三环原酰胺中的重叠 C(sp3)−CH3 键：CH−H••••O 氢键的证据
DOI：
10.1002/hlca.19890720531
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发表时间：
1989
影响因子：
1.8
通讯作者：
J. Dunitz
中科院分区：
文献类型：
--
作者：
P. Seiler;J. Dunitz
精确的，低温（81 K）X射线分析已作出的两个结晶修改的三环原酰胺1b：空间群为Pa 3（Z = 8）的立方三水合物，其中分子具有晶体学三重旋转对称性，以及空间群为P21/c（Z = 8）的无水单斜晶型，其中两个与结晶度无关的分子具有不同构型，一个是全反式（如在立方三水合物中），另一个是顺式、顺式、反式。在立方三水合物中，每个原酰胺分子通过OH... NH-键连接到H2O分子的三元组上。该结构的一个显著特征是中心C-CH 3键附近的几乎重叠构象。在无水晶体中，两种类型的分子具有其Me基团的正常交错取向。在三水合物中的Me取向的逆转是由于CH. O H-键合，这必须是更强和更定向的具体比以前假设的。
Accurate, low-temperature (81 K) X-ray analyses have been made for two crystalline modifications of the tricyclic orthoamide 1b: a cubic trihydrate in space group Pa3 (Z = 8), where the molecule has crystallographic threefold rotation symmetry, and an anhydrous monoclinic form in space group P21/c (Z = 8) where two symmetry-independent molecules have different configurations, one ail-trans. (as in the cubic trihydrate), the other cis, cis, trans. In the cubic trihydrate, each orthoamide molecule is attached to a triad of H2o molecules by OH…N H-bonds. A remarkable feature of this structure is the nearly eclipsed conformation about the central C-CH3 bond. In the anhydrous crystal, both types of molecule have the normal staggered orientation of their Me groups. The reversal of the Me orientation in the trihydrate is attributed to CH…O H-bonding, which must be much stronger and more directionally specific than has been previously assumed.