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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
Investigation of steric influences on hydrogen-bonding motifs in cyclic ureas by using X-ray, neutron, and computational methods

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 R2 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 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. The incredible bulk: A series of cyclic ureas has been studied to examine the influence of bulky substituents on the hydrogen-bonding motifs that form and the degree to which the urea group can be distorted to maintain strong intermolecular contacts.

computational chemistry, hydrogen bonds, neutron diffraction, self-assembly, supramolecular chemistry
1861-4728
2642-2651
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
McDonnell-Worth, Ciaran
9237ca3c-52b9-46e6-8e71-4815de0f5a86
Platts, James A.
2df1575c-ebd8-4dac-af9e-1590b47f0a73
Edwards, Alison J.
5ba9d596-9a31-4b76-8fdd-5209b8ca2d9a
Turner, David R.
bf5671a0-4a0a-41ed-b2f7-a539ccab65aa
McCormick, Laura J.
f1c2f8cd-adcc-4bbf-9289-0b33a006d2bb
McDonnell-Worth, Ciaran
9237ca3c-52b9-46e6-8e71-4815de0f5a86
Platts, James A.
2df1575c-ebd8-4dac-af9e-1590b47f0a73
Edwards, Alison J.
5ba9d596-9a31-4b76-8fdd-5209b8ca2d9a
Turner, David R.
bf5671a0-4a0a-41ed-b2f7-a539ccab65aa

McCormick, Laura J., McDonnell-Worth, Ciaran, Platts, James A., Edwards, Alison J. and Turner, David R. (2013) Investigation of steric influences on hydrogen-bonding motifs in cyclic ureas by using X-ray, neutron, and computational methods. Chemistry - An Asian Journal, 8 (11), 2642-2651. (doi:10.1002/asia.201300530).

Record type: Article

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 R2 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 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. The incredible bulk: A series of cyclic ureas has been studied to examine the influence of bulky substituents on the hydrogen-bonding motifs that form and the degree to which the urea group can be distorted to maintain strong intermolecular contacts.

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More information

e-pub ahead of print date: 8 August 2013
Published date: 1 November 2013
Keywords: computational chemistry, hydrogen bonds, neutron diffraction, self-assembly, supramolecular chemistry

Identifiers

Local EPrints ID: 438795
URI: http://eprints.soton.ac.uk/id/eprint/438795
ISSN: 1861-4728
PURE UUID: d665b284-3c58-46db-a5cd-8c93cbd56ff6
ORCID for Laura J. McCormick: ORCID iD orcid.org/0000-0002-6634-4717

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Date deposited: 24 Mar 2020 17:52
Last modified: 17 Mar 2024 04:01

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Contributors

Author: Ciaran McDonnell-Worth
Author: James A. Platts
Author: Alison J. Edwards
Author: David R. Turner

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