Structural and aromatic aspects for tautomerism of (Z)-6-((4-bromophenylamino)methylene)-2,3-dihydroxycyclohexa-2,4-dienone

KARABIYIK H., Petek H., Ocak İskeleli N., Albayrak C.

STRUCTURAL CHEMISTRY, vol.20, no.6, pp.1055-1065, 2009 (SCI-Expanded) identifier

  • Publication Type: Article / Article
  • Volume: 20 Issue: 6
  • Publication Date: 2009
  • Doi Number: 10.1007/s11224-009-9509-x
  • Journal Name: STRUCTURAL CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1055-1065
  • Keywords: Schiff base, Tautomerism, Resonance-assisted H-bond (RAHB), pi-electron coupling, HOMA, HYDROGEN-BONDS, SCHIFF-BASES, EQUILIBRIUM GEOMETRIES, ANALOGS, PROTON
  • Ondokuz Mayıs University Affiliated: Yes

Abstract

The molecular and crystal structure of (Z)-6-((4-bromophenylamino)methylene)-2,3-dihydroxycyclohexa- 2,4-dienone were determined by single crystal X-ray diffraction and spectroscopic methods. Molecules of the compound can be regarded as a resonance hybrid of cis-keto tautomer and zwitterionic form. Pairs of molecules of the compound generate pseudocyclic centrosymmetric R-2(2)(10) supramolecular synthons with the aid of O-H center dot center dot center dot O type intermolecular H-bonds. Stacking of R-2(2)(10) synthons along b-axis is stabilized by pi center dot center dot center dot pi interactions. Changes in both covalent topology and molecular geometry of the compound accompanying proton transfer were monitored by a relaxed PES scan with respect to hydroxyl bond length used as redundant internal coordinate. Quantum chemical studies at 6-311 + G(d,p) level reveal that bond lengths which are indicative to tautomerization process cannot reach their expected values even if proton transfer occurs in gas phase and pseudo-aromatic chelate ring formation has primary effect on the stabilization of NH tautomer. Resonance-assisted intramolecular H-bond affects the electronic state of its neighboring aromatic fragments.