Investigation of steric influences on hydrogen-bonding motifs in cyclic rreas by using x-ray, neutron, and computational methods
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Date
2013-11-01
Journal Title
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Publisher
Wiley-V C H Verlag GMBH
Abstract
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 R-2(2)(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 -carbon atom of the Nsubstituent. With the less-hindered substituents, methyl and ethyl, the anticipated tape motif is observed. When additional methyl groups are added onto the -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 -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 NHOC 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. © 2014, Wiley-VCH Verlag GmbH & Co. KGaA
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Keywords
Neutrons, Bonding, Diffraction, Neutron diffraction, Crystal structure, Hydrogen
Citation
McCormick, L. J., McDonnell-Worth, C., Platts, J. A., Edwards, A. J., & Turner, D. R. (2013). Investigation of steric influences on hydrogen-bonding motifs in cyclic rreas by using x-ray, neutron, and computational methods. Chemistry - An Asian Journal, 8(11), 2642-2651. doi:10.1002/asia.201300530