1H, 13C, and 15N Solid-State NMR Studies of Imidazole- and Morpholine-Based Model Compounds Possessing Halogen and Hydrogen Bonding Capabilities

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• 作者：Karim Bouchmella ; Sylvain G. Dutremez ; Bruno Alonso ; Francesco Mauri ; Christel Gervais
• 刊名：Crystal Growth & Design
• 出版年：2008
• 出版时间：November 5, 2008
• 年：2008
• 卷：8
• 期：11
• 页码：3941-3950
• 全文大小：367K
• 年卷期：v.8,no.11(November 5, 2008)
• ISSN：1528-7505

文摘

The halogen and hydrogen bonding interactions present in solid 1-(2,3,3-triiodoallyl)imidazole (1), morpholinium iodide (2), the 1:1 cocrystal 1-(2,3,3-triiodoallyl)imidazole·morpholinium iodide (3), morpholine (4), imidazole (5), and 1-(3-iodopropargyl)imidazole (6) have been investigated by solid-state ¹H, ¹³C, and ¹⁵N NMR spectroscopies. Comparison of the ¹⁵N CP MAS NMR spectrum of 3 with that of 2 indicates that protonated morpholine is present in solid 3, but this conclusion must be taken with caution as GIPAW calculations predict a ¹⁵N chemical shift for morpholine similar to that of the morpholinium cation. Conclusive evidence for the presence of a morpholinium cation in crystalline 3 was obtained by recording the static ¹⁵N NMR spectrum of this host−guest complex and comparing the morpholinium/morpholine part of the spectrum with the static spectra of 3 and 4 as obtained from ab initio calculations of NMR parameters based on the X-ray structures of these compounds. Concerning the imidazolyl group, ¹⁵N NMR spectroscopy has proven quite valuable to identify changes in the bonding situation of the C−NC nitrogen on passing from 1 to 3. In addition, slight differences are observed between the ¹⁵N chemical shifts of 1 and 6 that are ascribed to differences in halogen bond strengths between the two compounds. Attempts have also been made to study halogen bonding by ¹³C NMR spectroscopy, but this method did not provide exploitable results as signals corresponding to the sp and sp² carbon atoms bonded to iodine could not be observed experimentally. ¹H NMR spectroscopy is a powerful tool to study hydrogen bonding interactions of moderate energies such as ⁺NH₂···X (X = N, O, I). Indeed, we have found that the chemical shifts of the NH hydrogens were quite sensitive to the nature of X and to the N−H···X distance. This is demonstrated by the fact that the chemical shifts of the ⁺NH₂ protons of the morpholinium cation in 2 and 3 are noticeably different.