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Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution

Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution
Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution
Three Schiff bases generated by conventional condensation of a simple aminopolyol (TRIS) and 5-bromo- and 5-iodosalicylaldehyde, and 2-hydroxy-1-naphthaldehyde, have been fully characterized, both in solution and in the solid state. This study provides a complete analysis of imine–enamine equilibria, and sheds light onto the mechanism of hydrogen transfer, which has been controversial in the literature. Low-temperature X-ray diffraction accompanied by electron-density maps have further been complemented by theoretical studies at the B3LYP/6-31G* and M06-2X/6-311++G** levels. To ascertain the influence of crystal packing on tautomeric stability, the lattice has also been simulated by computation. This protocol involves the assessment of a supramolecular cluster around a core tautomer possessing either imine or enamine structures. Such an analysis, in full agreement with solid-state data, reveals the greater stability of zwitterionic structures for the salicyl derivatives. In contrast, these substances show preferential imine forms in solution, whereas the naphthyl-based compound exhibits a prevalent keto-enamine structure in all cases
tautomerism, Schiff bases, Density functional calculations, X-ray diffraction
1434-193X
3137-3145
Martínez, R. Fernando
25456861-d6d7-4964-ac9c-54f5a1e5c2ba
Ávalos, Martín
2d0b39c7-15a3-4f90-bdfb-8e4b6e69c64a
Babiano, Reyes
b7ffd91c-bacd-4372-ab99-fc30ac2450ae
Cintas, Pedro
29979233-8382-47a8-bde7-1faf4869308c
Jiménez, José L.
074cc8fd-9ea1-41fc-b8b6-551d26e5fcd3
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, Juan C.
2c06e379-89b3-46b1-95c8-7f5057732f9f
Martínez, R. Fernando
25456861-d6d7-4964-ac9c-54f5a1e5c2ba
Ávalos, Martín
2d0b39c7-15a3-4f90-bdfb-8e4b6e69c64a
Babiano, Reyes
b7ffd91c-bacd-4372-ab99-fc30ac2450ae
Cintas, Pedro
29979233-8382-47a8-bde7-1faf4869308c
Jiménez, José L.
074cc8fd-9ea1-41fc-b8b6-551d26e5fcd3
Light, Mark E.
cf57314e-6856-491b-a8d2-2dffc452e161
Palacios, Juan C.
2c06e379-89b3-46b1-95c8-7f5057732f9f

Martínez, R. Fernando, Ávalos, Martín, Babiano, Reyes, Cintas, Pedro, Jiménez, José L., Light, Mark E. and Palacios, Juan C. (2011) Schiff Bases from TRIS and ortho-hydroxyarenecarbaldehydes: structures and tautomeric equilibria in the solid state and in solution. European Journal of Organic Chemistry, 2011 (17), 3137-3145. (doi:10.1002/ejoc.201100275).

Record type: Article

Abstract

Three Schiff bases generated by conventional condensation of a simple aminopolyol (TRIS) and 5-bromo- and 5-iodosalicylaldehyde, and 2-hydroxy-1-naphthaldehyde, have been fully characterized, both in solution and in the solid state. This study provides a complete analysis of imine–enamine equilibria, and sheds light onto the mechanism of hydrogen transfer, which has been controversial in the literature. Low-temperature X-ray diffraction accompanied by electron-density maps have further been complemented by theoretical studies at the B3LYP/6-31G* and M06-2X/6-311++G** levels. To ascertain the influence of crystal packing on tautomeric stability, the lattice has also been simulated by computation. This protocol involves the assessment of a supramolecular cluster around a core tautomer possessing either imine or enamine structures. Such an analysis, in full agreement with solid-state data, reveals the greater stability of zwitterionic structures for the salicyl derivatives. In contrast, these substances show preferential imine forms in solution, whereas the naphthyl-based compound exhibits a prevalent keto-enamine structure in all cases

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More information

Published date: June 2011
Keywords: tautomerism, Schiff bases, Density functional calculations, X-ray diffraction
Organisations: Chemistry

Identifiers

Local EPrints ID: 336664
URI: http://eprints.soton.ac.uk/id/eprint/336664
ISSN: 1434-193X
PURE UUID: 47676397-6148-4b4d-b9e6-4686a274c942
ORCID for Mark E. Light: ORCID iD orcid.org/0000-0002-0585-0843

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Date deposited: 02 Apr 2012 14:13
Last modified: 18 Feb 2021 16:52

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