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

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 cisketo tautomer and zwitterionic form. Pairs of molecules of the compound generate pseudocyclic centrosymmetric R 2 2 ð10Þ supramolecular synthons with the aid of O-HÁÁÁO type intermolecular H-bonds. Stacking of R 2 2 ð10Þ synthons along b-axis is stabilized by pÁÁÁp 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.

Molecular structure of (Z)-6-[(5-chloro-2-hydroxyphenylamino) methylene]-3-(diethylamino)cyclohexa-2,4-dienone: A combined experimental and theoretical study

“…These bond lengths are in agreement with the corresponding values in the literature [10,47]. In this form, only the one ring of compound must be aromatic (see Fig.…”

“…These properties were investigated by Senier and Shepheard in 1909 for the first time [2,3]. The interest on ortho-hydroxy Schiff base compounds maintains its freshness for years and there are many published studies reporting the related features [4][5][6][7][8][9][10][11]. They have wide application in many fields, e.g., as ligands in the field of coordination chemistry [12,13], as starting materials in synthesis of important drugs (antibiotics, antiallergics, antitumors and antifungals) in pharmacy [14][15][16][17], as new organic materials in nanotechnology [18,19] and as elements for the design of various electronic devices such as optical switches and optical data storage devices [20,21].…”

The proton transfer process observed in the structure analysis and DFT calculations of (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol

“…Furthermore, synchronous decreasing in aromaticities of these adjacent fragments beyond this value causes an increase in aromaticity of the anisole ring. Similar tendencies are observed for another o-hydroxy aromatic Schiff base, (Z)-6-((4-bromophenylamino) methylene)-2,3-di-hydroxycyclohexa-2,4-dienone [19]. It can be mentioned here the presence of long-ranged p-electron coupling for the title compound so that p-electrons transfer from phenol toward anisole ring by means of chelate ring.…”

“…Experimental verification of this model is difficult, because keto and phenol tautomer of the compound are not sufficiently distinguishable from each other due to positional disorder when the tautomeric protons are located at the midpoint of the hydrogen bridge between O and N. In this study, distinct molecular geometries at the different stages in tautomerism of the title compound have been crystallographically examined and physical reasons underlying intramolecular proton transfer process has been investigated by quantum chemical calculations. Since modeling studies for tautomerism in salicylideneaniline derivatives by nonadiabatic proton transfer using a redundant internal coordinate have been introduced recently [19], the present treatise is of importance for relevant scientific community.…”

Crystal structure, spectral characterization, molecular modeling studies and structural effects of the proton transfer process for (E)-5-methoxy-2-[(3,4-dimethylphenylimino) methyl]phenol

“…Schiff bases have a wide range of applications in the fields of coordination chemistry, biochemistry, pharmacy, nanotechnology, optical devices and textiles [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In particular, the ortho-hydroxy class of Schiff bases has been attractive for physicists and chemists for many years because of its interesting photochromic and thermochromic features in the solid state.…”