AIM analysis of intramolecular hydrogen bonding in O-hydroxy aryl Schiff bases

AIM analysis was applied to study the changes in such topological parameters as the electron density at critical points of all the bonds of the molecule during the so-called nonadiabatic proton transfer in intramolecular hydrogen bonding in o-hydroxy aryl Schiff bases. Proton transfer is presented by a stepwise elongation and fixing of the hydroxyl bond with complete optimization of the rest of the parameters of the molecule by the B3LYP/6-311++G(d,p) method. A more detailed study of electron density changes at the critical points of the chelate and phenol rings in the stepwise proton-transfer process is presented. It was shown that the dependency of the electron density at the critical point of the chelate ring on tautomeric equilibrium is of a complicated character, whereas it is linear for the phenol ring. A complex study of the changes in the total electron density at the hydrogen bond, the quasi-aromatic ring, and in the whole molecule has been accomlished. The calculations of the intramolecular hydrogen bond by means of conformational and topological methods are discussed.     

Structure and characterization of N-(2-hydroxy-1-naphthylidene)threonine

Threonine Schiff base derived 2-hydroxy-1-naphthaldehyde and threonine has been isolated and investigated. The stoichiometry of this compound was derived from the results of elemental analyses, IR, ¹H-NMR and UV spectroscopic techniques. X-ray diffraction method was also used to obtain the single-crystal structure. The compound crystallizes in the space group P2₁ with cell dimensions a=5.109(2), b=11.334(2), and β=91(3)° with Z=2. The molecule has phenol-imine tautomeric form in the crystal structure. Some of bond lengths and angles found in the molecular structure are distorted due to π-electron delocalization and steric effect of naphthylidene and threonine groups.     

Differently coloured polymorphs of 4‐[(2‐nitrophenyl)azo]phenol

The crystal structures of the brown–yellow and orange polymorphs of the title compound, 4‐[(2‐nitro­phenyl)­diazenyl]­phenol, C₁₂H₉N₃O₃, have been determined and their visible reflection spectra recorded. Both structures adopt a stacking arrangement with interstack hydrogen bonds. Ab initio and semi‐empirical (AM1 and INDO‐CISD) calculations were performed in order to rationalize the difference in colour. It can be attributed neither to the subtle distinctions in molecular geometry nor to the effect of intermolecular electrostatic interactions. The most probable origin of this difference is the mixing of intramolecular n π* and intermolecular charge‐transfer excitations.     

Molecular and computational structure characterizations of (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol

The (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol compound was synthesized and characterized by X-ray Diffraction, IR and Electronic spectroscopy. X-Ray and IR results showed that the title compound preferred the enol form in solid state. UV-Vis absorption spectra of the title compound were recorded in different solvents. The results showed that the molecule existed only in enol form even in the solvent media. Electronic structure and spectroscopic properties of the title compound were investigated from calculative point of view. The gas phase geometry optimization was obtained based on X-ray geometry by DFT method with B3LYP applying 6-311G(d,p) basis set. Geometry optimizations in the solvent media were obtained with the same level of theory by the polarizable continuum model (PCM). TD-DFT calculations starting from the optimized geometry were made in both gas and solution phase to measure the excitation energies of enol and keto tautomers. Vibrational frequency and natural bond orbital analysis (NBO) were performed and the thermodynamic properties of the title compound were obtained at the optimized geometry with the same level of theory.     

PM3 semiempirical study and its comparison with X-ray crystal structure of 2-methyl-4-(4-methoxyphenylazo)phenol

The crystal and molecular structure of 2-methyl-4-(4-methoxyphenylazo)phenol have been determined by X-ray single crystal diffraction technique. The compound crystallizes in the monoclinic space group P2₁/c with a=9.7763(8) Å, b=11.3966(8) Å, c=11.9531(8) Å and β=108.752(6)°. In addition to the molecular geometry from X-ray experiment, its optimized molecular structure has been obtained with the aid of PM3 semiempirical quantum mechanical method, and then the corresponding geometric parameters were compared with those of X-ray crystallography. To determine conformational flexibility and crystal packing effects on the molecules, molecular energy profile of the title compound was obtained with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Crystal structure of the title compound is a fibroid structure constructed by C–H···O and O–H···N type intermolecular hydrogen bonds. The most favorable conformer of the title compound has been determined by the crystal packing effects and there is no steric hindrance during rotation around the selected torsion angles.     

Synthesis and structure of 1-[(3-hydroxybenzo[<Emphasis Type="Italic">b</Emphasis>]thiophen-2-yl)methylidene]-3-oxo-5-phenyl-1-pyrazolidinium-2-ide

Potentially tautomeric azomethine imine, 1-[(3-hydroxybenzo[b]thiophen-2-yl)methylidene]-3-oxo-5-phenyl-1-pyrazolidinium-2-ide has been prepared. According to X-ray diffraction, ¹H, ¹³C, and ¹⁵N NMR and electronic spectroscopy, the compound exists as 3-hydroxybenzothiophene structure containing intermolecular hydrogen bond between the hydroxy group and the carbonyl oxygen of the pyrazolidone ring in crystal state. Quantum chemical calculations predict the possibility of OH and NH tautomeric forms.     

Crystal structure, spectroscopy, and quantum chemical studies of (E)-2-[(2-chlorophenyl)iminomethyl]-4-trifluoromethoxyphenol

The Schiff base compound (E)-2-[(2-chlorophenyl)iminomethyl]-4-trifluoromethoxyphenol has been synthesized and characterized by IR, UV-vis, and X-ray single-crystal determination. The molecular geometry from X-ray experiment in the ground state has been compared using the density functional theory (DFT) with the 6-311++G(d,p) basis set. The calculated results show that the DFT can well reproduce the structure of the title compound. Using the TD-DFT method, electronic absorption spectra of the title compound have been predicted, and a good agreement is determined with the experimental ones. To investigate the tautomeric stability, optimization calculations at the B3LYP/6-311++G(d,p) level were performed for the enol and keto forms of the title compound. Calculated results reveal that its enol form is more stable than its keto form. The predicted nonlinear optical properties of the title compound are much greater than those of urea. The changes of thermodynamic properties for the formation of the title compound with the temperature ranging from 200 to 500 K have been obtained using the statistical thermodynamic method. At 298.15 K, the change of Gibbs free energy for the formation reaction of the title compound is -824.841 kJ/mol. The title compound can spontaneously be produced from the isolated monomers at room temperature. The tautomeric equilibrium constant is also computed as 3.85 × 10(-4) at 298.15 K for enol?keto tautomerization of the title compound. In addition, a molecular electrostatic potential map of the title compound was performed using the B3LYP/6-311++G(d,p) method.     

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

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 R₂² (10) R_{2}^{2} (10) supramolecular synthons with the aid of O–H···O type intermolecular H-bonds. Stacking of R₂² (10) R_{2}^{2} (10) synthons along b-axis is stabilized by π···π 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.     

Experimental and computational studies on zwitterionic (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate

The Schiff base compound (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate has been synthesised and characterized by IR, UV–Vis, and X-ray single-crystal determination. Ab initio calculations have been carried out for the title compound using the density functional theory (DFT) and Hartree–Fock (HF) methods at 6-31G(d) basis set. The calculated results show that the DFT/B3LYP and HF can well reproduce the structure of the title compound. Using the TD-DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental ones is determined. Molecular orbital coefficient analyses reveal that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. To investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d) level were performed for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable than NH form. In addition, molecular electrostatic potential and NBO analysis of the title compound were performed at B3LYP/6-31G(d) level of theory.     

2,4‐Bis(α,α‐di­methyl­benzyl)­phenol

The structure of the title compound, 2,4‐bis(1‐methyl‐1‐phenylethyl)phenol, C₂₄H₂₆O, was found to have a torsion angle of 129.95 (13)° for the C—C bond that connects the benzyl carbon to the phenol ring ortho to the OH group. A value of ～50° was expected from molecular mechanics calculations. Intermolecular interactions, in particular O—H?O and edge–face π bonding, may contribute to this discrepancy. Intramolecular O—H?π bonding is also observed.     

Preparation of New Photosensitive ZrO2 Gel Films Using Hydroxyl-Substituted Aromatic Ketones as Chemical Modification Reagents and their Patterning

ZrO₂ gel films were prepared from zirconium tetra-n-butoxide chemically modified with one of hydroxyl-substituted aromatic ketones and 1′-hydroxy-2′-acetonaphthone, by the sol-gel method. The obtained gel film showed an absorption band, characteristic of the π-π* transition of chelate ring, at around 410 nm. The band was shifted to longer wavelength region than those for the gel films using β-diketones. The reason is thought that the hydroxyl-substituted aromatic ketone has π-electron system to form the condensed chelate ring. The absorption band associated with the chelate ring gradually decreased in intensity with UV-irradiation using a high pressure mercury lamp. This indicates that the chelate ring dissociates by the UV-irradiation and that the gel film exhibits photosensitivity. Utilizing the photosensitivity, fine patterns (about 1 μm) could be fabricated by UV-irradiation through a mask and leaching.     

(Z)-1-[2-(二苯基碘化锡基)乙烯基]-1-环己醇的合成、晶体结构和性质

报道了标题化合物的合成、晶体结构及性质。该晶体属于单斜晶系，空间群为P2~1，晶胞参数a=0.9255(3)nm，b=1.0504(3)nm，c=1.0217(3)nm，β=100.99(2)°，V=0.9750nm^3，Z=2，D~c=1.790g/cm^3，R=0.025，晶体结构由直接法解出。标题化合物分子中的锡原子被配体的三个碳、一个碘和一个氧原子配位；配位原子是畸变的三角双锥构型；标题化合物具有与卤素发生取代反应而不发生加成反应的性质。     

1,1′,1′′-(2,4,6-Trihydroxybenzene-1,3,5-triyl)triethanone tautomerism revisited

It has recently been suggested that 1,1′,1′′-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone may be tautomeric. Using ¹³C NMR chemical shifts and deuterium isotope effects on ¹³C chemical shifts, it is demonstrated that this is not the case. This compound occurs as a strongly hydrogen bonded benzene structure with hydrogen bonds between OH groups and the acetyl groups in both non-polar and hydrogen donating solvents. Quantum-chemical calculations using MP2 and M06-2X methods show substantial preference for the phenol structure in both the gas phase, and in cyclohexane and methanol. In addition, conventional UV–vis spectroscopy data suggest not tautomeric, but aggregation behaviour of the molecule in methanol and acetonitrile.     

The Dianion of Heptalene

Heptalene – a very unstable compound – can be reduced by lithium at ?80° into its dianion. ¹H- and ¹³C-NMR. studies indicate that this dianion, contrary to the neutral molecule, has its π-bonds delocalized. The magnetic field induces in this species a large diamagnetic ring current. The dianion of heptalene is thermally very stable, much more so than the neutral compound. All these observations point to an appreciable stabilization energy associated with the 14°-electron system; this stabilization energy is probably large enough to impose a planar geometry to this dianion.     

Theoretical study of substituents effects on characteristics of resonance-assisted hydrogen bond in (Z)-(thionitrosomethylene)hydrazine and its derivatives in ground and electronic excited state

The molecular geometry, intramolecular hydrogen bond strength, vibrational frequencies, ¹H NMR chemical shift, and nuclear quadrupole resonance parameters of ¹⁴N, ³⁵S and ²H atoms and several well-established indices of aromaticity in (Z)-(thionitrosomethylene)hydrazine molecule and its derivatives were studied by density functional theory method. The results of calculations were obtained at B3LYP/6-311++G** level of approximation on model species, with the resonance-assisted hydrogen bonds. A set of simple and mostly common substituents having different properties in resonance effect according to values of substituents constants were chosen to simulate the influence of substitution in R position of title molecule on the quasi-delocalization and H-bonding. The following substituents have been taken into consideration: F, Cl, NO₂, OCH₃, OCF₃, SCH₃, SH, and OH. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. Also, the possible charge transfer and the topological properties of investigated molecule and its derivatives were studied by means of natural bond orbital and atoms in molecules (AIM) theory. The energy of the N–H···S interactions studied here was found medium in strength ( \( E_{\text{HB}}^{*} \)  = ?36.5 to ?45.3 kJ mol^?1). The electron density (ρ), Laplacian (?² ρ) properties and the total electron energy density (HC), estimated by AIM calculations, indicate that H···S bond possesses low ρ, positive ?² ρ and HC < 0 which are in agreement with partially covalent character of HB.     

An ab initio study of atomic interactions in monosubstituted benzenes

Molecules of monosubstituted benzenes XC₆H₅ (X = F, Cl, Br, OH, NH₂, CH₃, CH₂CH₃) were studied by the RHF/6-311G(d) method with full geometry optimization. Analysis of the molecular orbitals and contributions made to them by atomic orbitals, and also of the populations of the valence p orbitals of atoms in substituents X directly bonded to the aromatic ring showed that the features of the electron distribution in such molecules should not be attributed to the capability of the lone electron pairs of the heteroatoms in these substituents for p,π conjugation with the π-electron system of the molecule.     

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole: X-ray and DFT-calculated structures

2-Propylamino-5-[4-(2-hydroxy-3,5-dichlorobenzylideneamino) phenyl]-1,3,4-thiadiazole, formulated as C₁₈H₁₆Cl₂N₄OS (I), was synthesized. The crystal and molecular structure of (I) have been determined by ¹H-NMR, IR, and X-ray single crystal diffraction. The compound (I) crystallizes in the monoclinic, space group P2(1)/c with unit cell parameters a = 9.0576(2) Å, b = 24.3382(8) Å, c = 9.0585(2) Å, M _r = 407.31, V = 1851.13(9) Å³, Z = 4, R ₁ = 0.036, and wR ₂ = 0.096. Molecular geometry from X-ray experiment of (I) in the ground state has been compared using the density functional method (B3LYP) with 6-31G(d) basis set. To determine conformational flexibility, molecular energy profile of (I) was obtained by semi-empirical (PM3) calculations with respect to selected degree of torsional freedom, which was varied from ?180° to +180° in steps of 10°. The results are indicative that the Schiff base, which contains a thiadiazole ring, prefers to be in E-configuration. In addition, molecular electrostatic potential, frontier molecular orbitals, and natural bond orbitals analysis were performed by the B3LYP/6-31G(d) method.     

Density Functional Studies on Isonicotinato Lead(II) Complex [Pb(C5H4NCOO)2]

1 INTRODUCTION Recently, the chemistry of lead is of interest in relation to its toxicity and effects on intelligence in human populations[1~3]. The design of drugs to coun- teract the effects of lead poisoning requires estab- lishing the preferred ligands of Pb(II) and their ste- reochemistry. Consequently, synthesis of chelated- form antidotes for lead(II) ion toxicosis has attracted more and more attention, and numerous reports con- cerning experimental coordination chemistry of lead(…     

Crystal structure of [1,4-bis[1-(3,5-dichlorophenolato-2-ylmethyl)-ylpropylamino-kappa2N,O]piperazine-kappa2N,N']cobalt(II).

The X-ray crystal structure of the title complex, Co(Cl2bprpi) is described. In this complex the Co(II) center displays a distorted octahedral coordination geometry. The piperazine ring exhibits boat conformation, forming chelate rings and capping the Co atom. The N2-Col-N3 angle is 69.41(15) degrees, extremely smaller than 90 degrees. Because the small angle causes a large steric hindrance, the piperazine ring can be effective as an ion size-recognition site. The molecular structure is stabilized by intramolecular N-H...O hydrogen bonds and Cl...H contacts.