DFT calculations, spectroscopy and antioxidant activity studies on (E)-2-nitro-4-[(phenylimino)methyl]phenol.

We have reported synthesis and characterization of (E)-2-nitro-4-[(phenylimino)methyl]phenol by using X-ray crystallographic method, FT-IR and UV-vis spectroscopies and density functional theory (DFT). Optimized geometry and vibrational frequencies of the title compound in the ground state have been computed by using B3LYP with the 6-311G+(d,p) basis set. HOMO-LUMO energy gap, Non-linear optical properties and NBO analysis of the compound are performed at B3LYP/6-311G+(d,p) level. Additionally, as remarkable properties, antioxidant activity of the title compound (CMPD) has been determined by using different antioxidant test methods i.e. ferric reducing antioxidant power (FRAP), hydrogen peroxide scavenging (HPSA), free radical scavenging (FRSA) and ferrous ion chelating activities (FICA). When compared with standards (BHA, BHT, and α-tocopherol), we have concluded that CPMD has effective FRAP, HPSA, FRSA and FICA.

Molecular structure, quantum mechanical calculation and radical scavenging activities of (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds.

In this study, (E)-4,6-dibromo-2-[(3,5-dimethylphenylimino)methyl]-3-methoxyphenol and (E)-4,6-dibromo-2-[(2,6-dimethylphenylimino)methyl]-3-methoxyphenol compounds have been synthesized and characterized by using X-ray crystallographic method, FT-IR and Density functional method. The molecular geometry, vibrational frequencies of the title compounds in the ground state have been calculated by using B3LYP with the 6-31G(d,p) basis set. The tautomeric form of the compounds has been demonstrated by using single crystal X-ray method, FT-IR spectrometer and DFT method. In addition, HOMO-LUMO energy gap, molecular electrostatic potential map and NBO analysis of the compounds are performed at B3LYP/6-31G(d,p) level. It may be remarked that the free radical scavenging activities of the title compounds were assessed using DPPH, DMPD+, and ABTS+ assays. The obtained results show that especially compound 2 has effective DPPH (SC50 1.52±0.14 µg/mL), DMPD+ (SC50 1.22±0.21 µg/mL), and ABTS+ (SC50 3.32±0.17 µg/mL) scavenging activities compared with standards (BHA, rutin, and trolox).

Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol.

A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C15H15N1O2, reveals that the structure is adopted to its E configuration about the azomethine C=N double bond. The compound adopts a enol-imine tautomeric form with a strong intramolecular O-H⋯N hydrogen bond. The single crystal X-ray diffraction analysis at 296K crystallizes in the monoclinic space group P21/c with a = 13.4791(11) Å, b = 6.8251(3) Å, c = 18.3561(15) Å, α = 90°, ß = 129.296(5)°, γ = 90° and Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried out by FT-IR and UV-vis spectrometry. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the relocation of the electron density were determined. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties were also investigated. In addition, frontier molecular orbitals analysis have been performed from the optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (µ), electronegativity (χ), hardness (η), and softness (S), have been investigated.

Crystal structure, DFT and HF calculations and radical scavenging activities of (E)-4,6-dibromo-3-methoxy-2-[(3-methoxyphenylimino)methyl]phenol.

In this study, (E)-4,6-dibromo-3-methoxy-2-[(3-methoxyphenylimino)methyl]phenol has been synthesized and characterized by using X-ray technique and FT-IR experimentally and using B3LYP/6-31G(d,p) and HF/6-31G(d,p) methods theoretically. The intermolecular and intramolecular interactions of the title compound have been determined according to X-ray results. The molecular geometry, vibrational frequencies of the title compound in the ground state have been calculated using the density functional B3LYP and HF method with the 6-31G(d,p) basis set and calculated bond parameters and vibrational frequencies values show good agreement with experimental values. Theoretical and experimental results show that tautomeric form of the structure is phenol-imine form. Besides HOMO-LUMO energy gap, molecular electrostatic potential map were performed at B3LYP/6-31G(d,p) level. It is worthy note of that, the free radical scavenging activities of the title compound were assessed using DPPH˙, DMPD˙(+), and ABTS˙(+) assays. The obtained results show that the title compound has effective DPPH˙ (SC50 2.61±0.09 µg/mL), DMPD˙(+) (SC50 2.82±0.14 µg/mL), and ABTS˙(+) (SC50 4.91±0.18 µg/mL) radical scavenging activities when compared with standard antioxidants (BHA, rutin, and trolox).

Existence of a resonance hybrid structure as a result of proton tautomerism in (±)-(E)-4-bromo-2-[(2,3-dihydroxypropylimino) methyl]phenol racemate.

o-Hydroxy Schiff bases have two tautomers known as phenol-imine and keto-amine forms. In the present work, the tautomerism in (E)-4-Bromo-2-[(2,3-dihydroxypropylimino)methyl]phenol compound has been investigated by experimental (XRD, FT-IR and UV-vis) and computational (DFT and TD-DFT) methods. The X-ray diffraction (XRD) study reveals that the title compound favors a resonance hybrid structure of phenol-imine and keto-amine forms in the solid state rather than having these forms separately or jointly. Experimental UV-vis study of proton transfer process in solvent media (Benzene, DMSO and EtOH) shows the preference of phenol-imine form in benzene while both phenol-imine and keto-amine characteristics are present in EtOH and DMSO.

The prototropic tautomerism and substituent effect through strong electron-withdrawing group in (E)-5-(diethylamino)-2-[(3-nitrophenylimino)methyl]phenol.

The prototropic tautomerism in o-Hydroxy Schiff bases results in two forms called phenol-imine and keto-amine. The preference of a particular form by the compound changes in the solid and solvent media. The choice can also be regulated by a substituent with a different electron-donating or withdrawing group. In the present study, the above-mentioned factors are considered in the investigation of (E)-5-(diethylamino)-2-[(3-nitrophenylimino)methyl]phenol compound (an o-Hydroxy Schiff basis) by experimental (XRD, FT-IR and UV-vis) and computational (DFT and TD-DFT) methods. The results show that the title compound adopts only phenol-imine form in the solid and solvent media. This was attributed to the substituent effect through strong electron-withdrawing nitro group.

Survey of conformational isomerism in (E)-2-[(4-bromophenylimino)methyl]-5-(diethylamino)phenol compound from structural and thermochemical points of view.

In this study, (E)-2-[(4-bromophenylimino)methyl]-5-(diethylamino)phenol compound was investigated by mainly focusing on conformational isomerism. For this purpose, molecular structure and spectroscopic properties of the compound were experimentally characterized by X-ray diffraction, FT-IR and UV-Vis spectroscopic techniques, and computationally by DFT method. The X-ray diffraction analysis of the compound shows the formation of two conformers (anti and eclipsed) related to the ethyl groups of the compound. The two conformers are connected to each other by non-covalent C-H⋯Br and C-H⋯π interactions. The combination of these interactions is resulted in fused R(2)(2)(10) and R(2)(4)(20) synthons which are responsible for the tape structure of crystal packing arrangement. The X-ray diffraction and FT-IR analyses also reveal the existence of enol form in the solid state. From thermochemical point of view, the computational investigation of isomerism includes three studies: the calculation of (a) the rate constants for transmission from anti or eclipsed conformations to transition state by using Eyring equation, (b) the activation energy needed for isomerism by using Arrhenius equation, (c) the equilibrium constant from anti conformer to eclipsed conformer by using the equation including the change in Gibbs free energy. The dependence of tautomerism on solvent types was studied on the basis of UV-Vis spectra recorded in different organic solvents. The results showed that the compound exists in enol form in all solvents except ethyl alcohol.

Molecular structure, spectroscopic investigations, second-order nonlinear optical properties and intramolecular proton transfer of (E)-5-(diethylamino)-2-[(4-propylphenylimino)methyl]phenol: a combined experimental and theoretical study.

This work presents a combined experimental and theoretical study on an ortho-hydroxy Schiff base compound, (E)-5-(diethylamino)-2-[(4-propylphenylimino)methyl]phenol. The crystal structure and spectroscopic properties of the compound have been determined by using X-ray diffraction, IR and UV-vis spectroscopy techniques. The electronic structure, vibrational frequencies and electronic absorption spectra have been investigated from the calculative point of view. A relaxed potential energy surface scan has been performed based on the optimized geometry of OH tautomeric form to describe the potential energy barrier belonging to intramolecular proton transfer and to observe the effects of transfer on the molecular geometry. The second-order nonlinear optical properties have been investigated based on the first static hyperpolarizability (ß) by using the density functional theory.

Experimental and quantum chemical computational study of (E)-1-[5-(3,4-dimethylphenyldiazenyl)-2-hydroxyphenyl]ethanone.

In this work, the azo dye, (E)-1-[5-(3,4-dimethylphenyldiazenyl)-2-hydroxyphenyl]ethanone, has been synthesized and characterized by IR, and X-ray single-crystal determination. In the theoretical calculations, the stable structure geometry of the isolated molecule in gas phase was investigated under the framework of the density functional theory (B3LYP) with 6-31G (d, p). To designate lowest energy molecular conformation of the title molecule, the selected torsion angle was varied every 10° and the molecular energy profile was calculated from -180° to +180°. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and thermodynamic properties were described from the computational process. In addition to these calculations, we were investigated solvent effects on the nonlinear optical properties (NLO) of the title compound.

Single stranded helical chains of C-H⋯π interactions further connected by halogen-halogen interactions of type I to construct supramolecular structure of (E)-5-(diethylamino)-2-[(4-iodophenylimino)methyl]phenol compound.

In this study, (E)-5-(diethylamino)-2-[(4-iodophenylimino)methyl]phenol compound was investigated from the point of stacking interactions assembling the supramolecular network, conformational isomerism and tautomerism. For this purpose, X-ray diffraction, FT-IR and UV/Vis spectroscopic techniques were used, giving the following structural and spectroscopic properties of the compound: The title compound has two conformers (anti and eclipsed) in the crystal structure resulting from rotation about C-N single bond of ethyl group. Both conformers prefer enol form in the solid state, adopting E configuration about the CN double bond. The supramolecular architecture of the compound is constructed by two non-covalent interactions as C-H⋯π and halogen-halogen interactions. The repetition of C-H⋯π interactions is resulted in a single-stranded helical structure. The helical structures are further connected by C-I⋯I-C interactions of Type I to construct the two dimensional supramolecular network defined as (6,3)-net in Wells nomenclature. The title compound adopts both enol and keto forms in EtOH (a polar and protic solvent) while enol form is preferred in the solid state.

Synthesis, spectroscopic characterizations and quantum chemical computational studies of (Z)-4-[(E)-p-tolyldiazenyl]-6-[(2-hydroxyphenylamino)methylene]-2-methoxycyclohexa-2,4-dienone.

In this study, the molecular structure and spectroscopic properties of title compound were characterized by X-ray diffraction, FT-IR and UV-vis spectroscopies. These properties of title compound were also investigated from calculative point of view. The X-ray diffraction and FT-IR analyses reveal the existence of keto form in the solid state. UV-vis spectra were recorded in different organic solvents. The results show that title compound exists in both keto and enol forms in DMSO, EtOH but it exists in enol form in benzene. In addition, the title compound in DMSO showed new absorption band at 436 nm due to the high ionizing effect of this solvent. The geometry optimization of title compound in gas phase was performed using DFT method with B3LYP applying 6-311G(d,p) basis set. TD-DFT calculations starting from optimized geometry were carried out in gas phase to calculate excitation energies of title compound. The non-linear optical properties were computed with the same level of theory and title compound showed a good second order nonlinear optical property. In addition, thermodynamic properties were obtained in the range of 100-500 K.

Synthesis, spectroscopic characterizations and quantum chemical computational studies of (Z)-4-[(E)-(4-fluorophenyl)diazenyl]-6-[(3-hydroxypropylamino)methylene]-2-methoxycyclohexa-2,4-dienone.

In this study, the molecular structure and spectroscopic properties of the title compound were characterized by X-ray diffraction, FT-IR and UV-vis spectroscopies. These properties were also investigated using DFT method. The most convenient conformation of title compound was firstly determined. The geometry optimizations in gas phase and solvent media were performed by DFT methods with B3LYP adding 6-31G(d) basis set. The differences between crystal and computational structures are due to crystal packing in which hydrogen bonds play an important role. UV-vis spectra were recorded in different organic solvents. The results show that title compound exists in both keto and enol forms in DMSO, EtOH but it tends to shift towards enol form in benzene. The polar solvents facilitate the proton transfer by decreasing the activation energy needed for Transition State. The formation of both keto and enol forms in DMSO and EtOH is due to decrease in the activation energy. TD-DFT calculations starting from optimized geometry were carried out in both gas and solution phases to calculate excitation energies of the title compound. The non-linear optical properties were computed at the theory level and the title compound showed a good second order non-linear optical property. In addition, thermodynamic properties were obtained in the range of 100-500K.

Probing the compound (E)-5-(diethylamino)-2-[(4-methylphenylimino)methyl]phenol mainly from the point of tautomerism in solvent media and the solid state by experimental and computational methods.

In this study, the molecular structure and spectroscopic properties of (E)-5-(diethylamino)-2-[(4-methylphenylimino)methyl]phenol were characterized experimentally by X-ray diffraction, FT-IR and UV-vis spectroscopic techniques and computationally by DFT method. It is concluded on the basis of X-ray diffraction and FT-IR analyses that the title compound exists in enol form in the solid state. UV-vis spectra of the title compound were recorded in different organic solvents to investigate the dependence of tautomerism on solvent types. The tautomerism-solvent relation was also studied by computational methods to have more insight on structural properties. The geometry optimization of the title compound in gas phase was performed by using DFT (B3LYP) method with 6-311G(d,p) basis set. The geometry optimizations in solvent media were carried out at the same theory level by the polarizable continuum model (PCM). In the calculation of excitation energies, TD-DFT calculations were carried out in both gas and solution phases. The computational investigation of non-linear optical properties indicates that the title compound has a good second order nonlinear optical property. The thermodynamic properties were obtained in the range of 100-500 K.

5-Diethyl-amino-2-[(E)-(4-eth-oxy-phen-yl)imino-meth-yl]phenol.

The title compound, C(19)H(24)N(2)O(2), adopts the phenol-imine tautomeric form. An intra-molecular O-H⋯N hydrogen bond results in the formation of a six-membered ring. The aromatic rings are oriented at a dihedral angle of 17.33 (16)°. Inter-molecular C-H⋯π inter-actions occur in the crystal.

1-{5-[(E)-(4-Propyl-phen-yl)diazen-yl]-2-hy-droxy-phen-yl}ethanone.

The mol-ecular geometry of the title compound, C(17)H(18)N(2)O(2), displays an E configuration with respect to the azo group. The dihedral angle between the aromatic rings is 10.39 (4)°. In the mol-ecule, an intra-molecular O-H⋯O hydrogen bond generates an S(6) ring motif.

1-{5-[(E)-(2-Fluoro-phen-yl)diazen-yl]-2-hy-droxy-phen-yl}ethanone.

Theere are two independent mol-ecules in the asymmetric unit of the title compound, C(14)H(11)FN(2)O(2), each with a trans configuration with respect to the azo double bond. The dihedral angle between the aromatic rings is 17.21 (2)° in one mol-ecule and 19.06 (2)° in the other. Each of the independent mol-ecules has an intra-molecular O-H⋯O hydrogen bond. In the crystal, mol-ecules are stacked along [100].

Spectroscopic investigations and quantum chemical computational study of (E)-4-methoxy-2-[(p-tolylimino)methyl]phenol.

In this work the electronic structure of (E)-4-methoxy-2-[(p-tolylimino)methyl]phenol has been characterized by the B3LYP/6-31G(d) level by using density functional theory. The experimental infrared and electronic absorption spectra have been obtained and compared with the theoretically obtained ones. Molecular electrostatic potential map has been evaluated; natural bond orbital and frontier molecular orbitals analysis have been performed from the optimized geometry. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model. The non-linear optical properties have been computed with the same level of theory. In addition, the changes of thermodynamic properties have been obtained in the range of 100-500 K.

3-Diethyl-amino-6-[(Z)-(4-hy-droxy-anilino)methyl-idene]cyclo-hexa-2,4-dienone.

In the mol-ecule of the title compound, C(17)H(20)N(2)O(2), the aromatic rings are oriented at a dihedral angle of 6.23 (22)°. Intra-molecular N-H⋯O hydrogen bonding involving the amine H atom and the carbonyl O atom affects the conformation of the mol-ecule. One of the ethyl arms is disordered over two conformations, with occupancies of 0.59 (2) and 0.41 (2). The crystal packing is stabilized by inter-molecular C-H⋯O and O-H⋯O hydrogen bonds, and weak C-H⋯π inter-actions.

(E)-2-[(2-Ethyl-phen-yl)imino-meth-yl]-6-methoxy-phenol.

The mol-ecule of the title compound, C(16)H(17)NO(2), adopts the phenol-imine tautomeric form with a strong intra-molecular O-H⋯N hydrogen bond and an E conformation with respect to the azomethine C=N bond. The dihedral angle between the aromatic rings is 21.23 (9)°. The ethyl group is disordered over two orientations with occupancies of 0.598 (6) and 0.402 (6). In the crystal, the mol-ecules are linked into chains along the b axis by C-H⋯π inter-actions.

(E)-5-Meth-oxy-2-(o-tolyl-imino-meth-yl)phenol.

In the title compound, C(15)H(15)NO(2), the phenol group make dihedral angles of 2.4 (2) and 24.1 (9)° with the imine linkage (-C=N-) and the phenyl group, respectively, and the mol-ecule adopts the enol-imine tautomeric form, so the mol-ecular structure is stabilized by a strong intra-molecular O-H⋯N hydrogen bond. The crystal structure features a weak C-H⋯π inter-action.