Investigation of the azo-hydrazone tautomeric equilibrium in an azo dye involving the naphthalene moiety by UV–vis spectroscopy and quantum chemistry (original) (raw)
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Arabian Journal of Chemistry, 2015
The state of the tautomeric equilibria of eleven arylazo pyridone dyes was evaluated from UV-Vis absorption spectra with the aid of the quantum mechanical modeling. NMR analysis and theoretical calculations, by using PCM/xB97X-D/6-311G(d,p) method, confirmed that prepared compounds exist mainly in Hydrazo form. Internal hydrogen bonding in Hydrazo tautomer, analyzed by AIM topological analysis and total electron density at the bond critical point (BCP), confirmed a presence of strong hydrogen bond which contributes to higher stability of Hydrazo form. Linear solvation energy relationships (LSERs) rationalized solvent influence on solvatochromism of all compounds in Hydrazo form and K T by using Kamlet-Taft model. Linear free energy relationships (LFERs) were applied to the substituent-induced NMR chemical shifts (SCS) using SSP (single substituent parameter) and DSP (dual substituent parameter) model. Density plots over the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) energy surface provide information on the charge transfer during excitation. The molecular electrostatic potential (MEP)
Effect of Cooperative Hydrogen Bonding in Azo−Hydrazone Tautomerism of Azo Dyes
The Journal of Physical Chemistry A, 2007
Azo-hydrazone tautomerism in azo dyes has been modeled by using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level of theory. The most stable tautomer was determined both for model compounds and for azo dyes Acid Orange 7 and Solvent Yellow 14. The effects of the sulfonate group substitution and the replacement of the phenyl group with naphthyl on the tautomer stability and on the behavior in solvent have been discussed. Intramolecular hydrogen bond energies have been estimated for the azo and hydrazone tautomers to derive a relationship between the tautomer stability and the hydrogen bond strength. The transition structures for proton transfer displayed resonance assisted strong hydrogen bonding properties within the framework of the electrostatic-coValent hydrogen bond model (ECHBM). Evolution of the intramolecular hydrogen bond with changing structural and environmental factors during the tautomeric conversion process has been studied extensively by means of the atoms-in-molecules (AIM) analysis of the electron density. The bulk solvent effect was examined using the self-consistent reaction field model. Special solute-solvent interactions were further investigated by means of quantum mechanical calculations after defining the firstsolvation shell by molecular dynamics simulations. The effect of cooperative hydrogen bonding with solvent molecules on the tautomer stability has been discussed.
Spectral studies and molecular orbital PPP-calculations of some azo-dyes
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2002
The UV, IR and 1H-NMR spectra of some 4-(R-phenyl azo) 1-hydroxy 2-naphthoic acid derivatives are studied. The effects of substituent groups and the solvent polarity on electronic spectral, IR bands and 1H-NMR proton chemical shifts are considered, the molecular orbital calculations obtained are rationalized quantitatively with that obtained practically using the PPP-model with configuration interaction (CI).
Journal of Molecular Liquids, 2014
Five novel azo-hydrazone tautomeric dyes 3a-e were synthesized in two steps using Knoevenagel condensation and azo coupling reaction. The structures of the new compounds were confirmed by UV-vis, IR and NMR spectroscopies. Spectral data indicated that these dyes exist predominantly in the hydrazone tautomeric form in solutions. In addition, the absorption ability of the dyes showed that the solvent effect on UV-vis absorption spectra is complex and effectively depends on the nature of the substituent on the diazo component. The effects of acidic and basic media on the visible absorption spectra of the dyes were also examined. The antibacterial and antioxidant activities of the dyes were characterized using the agar well diffusion and ferric reducing antioxidant power (FRAP) methods, respectively. The synthesized dyes exhibited both antioxidant and antibacterial activities.
Acta Physica Polonica A, 2016
The optimized geometrical structures, infrared spectra, molecular electrostatic potential, natural bond orbital and nonlinear optical properties of 5-phenylazo-6-hydroxy-4-phenyl-3-cyano-2-pyridoine (1) and 5-(4-bromophenylazo)-6-hydroxy-4-phenyl-3-cyano-2-pyridoine (2) dyes with a detailed study on the azo-hydrazone tautomerism in the ground state have been investigated by density functional theory using B3LYP functional with 6-31G(d,p) basis set. Vibrational modes are assigned with the help of vibrational energy distribution analysis program. Highest occupied molecular orbital and lowest unoccupied molecular orbital energies of the (1) and (2) compounds with azo and hydrazone forms were calculated with the same method and basis set. Molecular parameters like global hardness (η), global softness (σ) and electronegativity (χ) were calculated with the results obtained from the highest occupied and lowest unoccupied molecular orbital energies. Nonlinear optical parameters (mean polarizability (α), the anisotropy of the polarizability (∆α) and the mean first-order hyperpolarizability (β)) of the title compounds were investigated theoretically. The atomic charges, electronic exchange interaction, and charge delocalization of the molecules have been studied by natural bond orbital analysis.
Effect of Solvent on Azo-Hydrazonetautomerism of 2-Hydroxy-5-(4-Nitrophenylazo) Benzaldehyde
2015
Azo dye has been synthesized having Donor-p-Acceptor (D-p-A) system to study the effect of solvent on the azo-hydrazone tautomerism. The relative stabilities of azo and hydrazone tautomer are examined by means of UV-Vis spectroscopic technique and are correlated with the solvent properties in neat organic solvents and in different binary solvent mixture. Due to the presence of intramolecular H-bonding, azo form predominates in most of the nonpolar and polar protic solvents. Presence of low energy CT band in basic solvents like DMF is due to the predominance of anionic hydrazone form stabilized through the lengthening of the conjugated system. In the binary solvent mixtures, preferential solvation occurs due to specific solute-solvent interaction. The microenvironment surrounding the dye molecules played a major role in the stability of one tautomer relative to the other.A good understanding of the properties of specific azo dyes in different medium lead to the design of new azo dye ...
Solvent Effects on the Electronic Spectra of Some Heterocyclic Azo Dyes
Bulletin of the Korean Chemical Society, 2014
The influence of solvent polarity on the absorption spectra of some synthesized azo dye with heterocyclic moieties and -naphthol (1-3) have been investigated using a UV-Visible spectrophotometer. The spectral characteristics of the azo dyes (1-3) in different solvents at room temperature were analyzed. The solvatochromic empirical variables like * , , and have been used to discuss the solvatochromic behaviour of the dyes and to evaluate their contributions to the solute-solvent interactions. A multi-parameter regression model for quantitative assessment of the solute/solvent interaction and the absorption has been used to explain the solvent effect on azo dyes (1-3).
A study on optimum transition state and tautomeric structures of a bis-heterocyclic monoazo dye
Indian Journal of Physics, 2014
In this study, possible tautomeric forms and ground state conformers of a bis-heterocyclic monoazo dye, 4-[ethyl 4 0-methyl-5 0-(phenylcarbamoyl)thiophene-3 0-carboxylate-2 0-ylazo]-3-methyl-1H-pyrazolin-5-one, have been calculated using density functional theory methods with 6-31G (d) basis set. 1 H and 13 C chemical shifts of tautomeric forms have been calculated. Calculated vibrational frequencies and chemical shifts have been compared with corresponding experimental data. Using time-dependent Hartree-Fock method, electronic absorption spectrum of title compound has been calculated and compared with experimental maximum wavelength data. Quantum Synchronous Transit2 approaches have been used for finding the optimum transition state and tautomeric forms of studied molecule. Calculations have shown that the most probable preferential form of this molecule in ground state is hydrazo-keto form. The calculations of frontier molecular orbitals and first order hyperpolarizability have also confirmed this stability.
Spectrochimica Acta Part A Molecular Spectroscopy
The spectral behaviour of six a-hydroxy azo compounds has been investigated in solution. The bands appearing in the u.v. and visible regions are assigned to possible electronic transitions. Azo compounds containing pyrazoione and acetyl or ester moieties are found to exist mainly in the hydrazo form in solution, while those containing the naphthol moiety exist in the azo-hydrazone tautomeric equilibrium. The solvatochromic behaviour of the compounds is investigated by studying their spectra in organic solvents of different polarities. The acidity constants are determined from the spectra of the compounds in aqueous ethanolic solutions of varying pH values.