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Revealing the Configuration and Crystal Packing of Organic Compounds by Solid‐State NMR Spectroscopy: Methoxycarbonylurea, a Case Study
Author(s) -
Macholl Sven,
Börner Frank,
Buntkowsky Gerd
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400191
Subject(s) - intermolecular force , molecule , chemistry , ab initio , crystallography , hydrogen bond , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry
The molecular configuration and intermolecular arrangement of polycrystalline methoxycarbonylurea (MCU) has been studied by a combination of chemical editing, rotational echo double resonance (REDOR) spectroscopy and ab initio calculations. From the multispin IS n REDOR experiments several dipolar couplings were determined and converted into distance constraints. Intra‐ and intermolecular dipolar couplings were distinguished by isotope dilution. The configuration of the MCU molecule can be determined from three torsion angles Ψ 1 , Ψ 2 , and Ψ 3 . Ab initio calculations showed that these angles are either 0° or 180° ( Z or E ). From the REDOR experiments, the E configuration was found for Ψ 1 and Ψ 2 and the Z configuration for Ψ 3 . Thus the configuration of MCU in the solid state was determined to be EEZ . Distance constraints for the intermolecular arrangement of MCU were obtained by performing REDOR experiments on 13 C 15 N 2 MCU with different degrees of isotope dilution and on a cocrystallized 1:1 mixture of 13 C(urea) MCU and 15 N(amide) MCU. By combining these distance constraints with molecular modeling, three different possible packing motifs for MCU molecules were found. The molecules in these motifs are arranged as linear chains with methoxy groups at the borders of the chains. All the intermolecular hydrogen bond donors and acceptors in the interior of the chain are saturated.