Substituent and solvent effects on the rate of the reaction of 2-methyl-4-phenyl-thiazole ethiodide with substituted benzaldehydes

Condensation of 2-methyl-4-phenyl-thiazole ethiodide (1) with aromatic aldehydes in presence of piperidine as base catalyst has been studied kinetically at different temperatures. The rate in presence of low concentration of piperidine (<0.5M) is found to be represented by the third order equationv=k [1] [aldehyde] [piperidine]. On the other hand the rate in presence of 1.013M piperidine is represented by the second-order equation:v=k [1] [aldehyde]. It is concluded from the kinetic results that the dehydration step of the intermediate aldol compound is the rate determining step of the reaction. The dependence of the mechanism of the reaction and the thermodynamic parameters of activation on the molecular structure of the various aromatic aldehydes used is discussed. In various organic solvents, the rate of the reaction increases as the dielectric constant of the medium is increased. The energy of activation and the thermodynamic parameters of activation were calculated and discussed in terms of solvent properties.

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Substituenten- und Lösungsmittel-Effekte auf die Geschwindigkeit der Reaktion zwischen 2-Methyl-4-phenylthiazol-ethiodid und substituierten Benzaldehyden

Zusammenfassung Die Kinetik dieser Kondensation wurde bei verschiedenen Piperidinkonzentrationen (basischer Katalysator), unter Variation der Temperatur und in Abhängigkeit von der Polarität des Lösungsmittels für verschiedene substituierte Benzaldehyde untersucht. Bei niedriger Piperidinkonzentration gehorcht die Reaktion einer Gleichung dritter Ordnung:v=k [Thiazo] [Ald.] [Pip.]; bei großer Konzentration (1.013M) gilt eine Gleichung zweiter Ordnung:v=k [Thizol] [Ald.]. Es wird ein Mechanismus vorgeschlagen, wobei der geschwindigkeitsbestimmende Schritt die Dehydratisierung des intermediär gebildeten Aldols ist. Aktivierungsenergien und andere thermodynamische Parameter wurden bestimmt und im Hinblick auf die Lösungsmittelpolarität diskutiert.

     

Preparation and IR-spectroscopic study of charge transfer complexes of naphthalene derivatives with some tri- and di-nitrobenzenes

The charge transfer complexes of naphthalene and some of its derivatives with some trinitro- and dinitrobenzenes are prepared and investigated by irspectroscopy. The shifts in the bands due to functional groups as well as the _CH bands of both donor and acceptor are found to be indicative for the type of bonding in the charge transfer complex.

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Darstellung und IR-spektroskopische Untersuchungen an Charge Transfer Komplexen von Naphthalinderivaten mit Di- und Tri-nitrobenzolen

Zusammenfassung Aus den Verschiebungen der Bandenlagen bei der Komplexierung, bzw. aus der Abhängigkeit der Bandenlagen von den funktionellen Gruppen, wird der Bindungstyp der Charge-Transfer-Komplexe ermittelt.

     

Studies on the complex formation of N,N-diethylglycine with copper(II) in acetonitrile

The formation of copper(II) complexes with N,N-diethylglycine in acetonitrile has been investigated by visible, infrared as well as NMR spectral techniques. It has been found that 11 and 12 complexes are formed. In both compounds nitrogen and carboxyl oxygen of ligand molecules are involved in coordination. The stability constants are reported.

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Untersuchungen von Kupfer(II)-Komplexen mit N,N-Diethylglycin in Acetonitril

Zusammenfassung Die Bildung von Kupfer(II)-Komplexen mit N,N-Diethyglycin in Acetonitril wurde mit Hilfe von UV-VIS, IR- und NMR-Spektroskopie untersucht. Es wurde festgestellt, daß sich Komplexe der Zusammensetzung 11 und 12 bilden. In beiden Verbindungen koordinieren Stickstoff und Carboxylsauerstoff der Liganden. Die Stabilitätskonstanten wurden bestimmt.

     

Crystal structure and spectra of the Ni(II) complex of pyridine-2,6-dithio-carbomethylamide

The crystal structure of the paramagnetic bis(pyridine-2,6-dithiocarbomethylamide) nickel(II) nitrate (NiPDTA) is described: C₁₈H₂₂N₆S₄·(NO₃)₂·(H₂O)_1,5, monoclinic, C2/c,Z=4,a=14.705 (3) Å,b=23.254 (8) Å,c=8.383 (3) A, =98.18 (2)°,d _x=1.55 gcm^–3,d _m=1.53 gcm^–3. The structure was solved withPatterson and differenceFourier techniques and refined to a residual ofR=0.053. The nickel is surrounded by a square bipyramidal coordination of four thioamide sulfur atoms and two pyridine nitrogen atoms. Vibrational and electronic band positions for this compound are discussed.

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Kristallstruktur und Spektren des Pyridin-2,6-dithiocarbomethylamid Nickel(II)-Komplexes

Zusammenfassung Die Kristallstruktur des paramagnetischen bis(Pyridin-2,6-dithiocarbomethylamid) Nickel(II)-nitrats (NiPDTA) wurde bestimmt. C₁₈H₂₂N₆S₄Ni·(NO₃)₂·(H₂O)_1,5, monoklin, C2/c,Z=4,a=14,705 (3) Å,b=23,254 (8) Å,c=8,383 (3) A, =98,18 (2)°,d _x=1,55gcm^–3,d _m=1,53gcm^–3. Das Phasenproblem wurde mittelsPatterson-und Differenz-Fourier-Synthese bestimmt und die Struktur bis zu einem kristallographischenR-Faktor vonR=0.053 verfeinert. Das Nickel-Atom ist von vier Thioamid-Schwefelatomen und zwei Pyridin-Stickstoffatomen in quadratisch-bipyramidaler Anordnung umgeben. Schwingungsspektren und Anregungsspektren des Komplexes werden diskutiert.

     

[4+2]-Cyclodimer of sabinone: formation,crystal structure,and NMR spectra

Oxidation of (+)-sabinol, (1S,3R,5S)-1-isopropyl-4-methylidenebicyclo[3.1.0]hexan-3-ol, by active MnO₂ afforded not the expected sabinone but only its [4+2]-cyclodimer. The molecular structure of the latter was established by X-ray diffraction analysis. The ¹H and ¹³C NMR spectra of this cyclodimer were interpreted using 2D NMR spectroscopy.     

Theoretical study on contribution of charge transfer effect to surface-enhanced Raman scattering spectra of pyridine adsorbed on Ag(n) (n = 2-8) clusters

We investigate surface-enhanced Raman scattering (SERS) spectra of pyridine–Ag_n (n = 2–8) complexes by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. In simulated normal Raman scattering (NRS) spectra, profiles of pyridine–Ag_n (n = 2–8) complexes are analogical with that of isolated pyridine. Nevertheless, calculated pre-SERS spectra are strongly dependent on electronic transition states of new complexes. Wavelengths at 335 nm, 394.8 nm, 316.9 nm and 342.6 nm, which are nearly resonant with pure charge transfer excitation states, are adopted as incident light when simulating pre-SERS spectra for pyridine–Ag_n (n = 2–8) complexes, respectively. We obtain enhancement factors from 10³ to 10⁵ in pre-SERS spectra compared with corresponding NRS spectra. The obvious increase in Raman intensities mainly result from charge transfer resonance Raman enhancement. A charge difference densities (CDDs) methodology is adopted in describing chemical enhancement mechanism. This methodology aims at visualizing charge transfer from Ag_n (n = 2–8) clusters to pyridine on resonant electronic transition, which is one of the most direct evidences for chemical enhancement mechanism.     

Spectrophotometric study of complex formations between 1-(2-pyridylazo)-2-naphthol (PAN) and some metal ions in organic solvents and the determination of thermodynamic parameters

The complexation reactions between Ni(2+), Co(2+) and Zn(2+) metal ions with PAN in methanol (MeOH), acetonitrile (AN) and dimethyl sulfoxide (DMSO) were studied using a spectrophotometric method. The stability constants of the resulting complexes were determined from computer fitting absorbance mole-ratio data. The results revealed that the stability constants of complexes are varying in order of Ni(2+)相似文献   

Spectroscopic studies on the formation of charge transfer complexes of l-phenylalanine with 2,3,5-trichloro-6-alkoxy-1,4-benzoquinones in aqueous medium

UV–Vis, FT-IR, LC–MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of l-phenylalanine with new π-acceptors, 6-alkoxy-2,3,5-trichloro-1,4-benzoquinones. The interaction of these quinones with l-phenylalanine (LPA) yielding radical ion pair was found to proceed through the formation of donor–acceptor complex. The stoichiometry of the complexes was determined by Job’s continuous variation method and was found to be 1:1 in all the cases. Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological conditions (pH = 7). Fluorescence quenching studies indicated that the interaction between the donors and the acceptor is spontaneous. Correlation of association constants of the CT complexes with Taft’s polar and steric constants indicated that the electronic effects of the substitutions play a significant role in governing the reactivity of the quinones when compared to steric factors.     

Synthesis of 4-aryloxy-7-nitrobenzofurazan derivatives from 4-chloro-7-nitrobenzofurazan and various phenoxide anions (including pharmaceuticals) in the presence of crown ethers

4-Chloro-7-nitrobenzofurazan reacts by nucleophilic substitution with phenoxide anions derived from estriol (2c), ethynylestradiol (2d), phenol (3e), guaiacol (3f), 2,6-dimethoxyphenol (3g), eugenol (3h), isoeugenol (3i), the cytostatic Etoposide (4), and Reichardt’s betaine (5) in the presence of crown ethers affording the corresponding 4-aryloxy-7-nitrobenzofurazan derivatives 6c, 6d, 7e-7i, 8, and 9. The structure of these compounds was confirmed by NMR spectra. Hydrophobicity/hydrophilicity parameters were investigated by reverse phase thin-layer chromatography.     

Wet-chemical synthesis of crystalline BaTiO3 from stable chelated titanium complex: formation mechanism and dispersibility in organic solvents

Crystalline barium titanate nanoparticles were synthesized in solution at low temperature (70 degrees C) from acetylacetone chelated titanium complex and barium hydroxide. Very fine crystalline solids were characterized to cubic phase of BaTiO(3) by X-ray diffraction studies of the air-dried samples. It was observed that the crystalline barium titanate was formed in solution at Ba/Ti molar ratio > or =2.5. The dependence of the reaction temperature and the Ba(OH)(2) concentration (in terms of Ba/Ti molar ratio) on formation of crystalline BaTiO(3) in solution-phase was studied, and a plausible mechanism toward the formation of crystalline BaTiO(3) was also proposed. Crystallite sizes of the BaTiO(3) were found to be in the range 33-50 nm, while the average particle sizes, measured by dynamic light scattering method were in the range 70-100 nm. The crystalline BaTiO(3) prepared from acetylacetone chelated titanium complex was highly dispersible in organic medium such as N-methyl-2-pyrillidone (NMP) and N,N-dimethyl formamide (DMF).     

Measurement of inter- and intramolecular charge transfer in the complex N2ICl from analysis of halogen nuclear quadrupole hyperfine structure in the rotational spectrum

The ground-state rotational spectra of two isotopomers ¹⁵N₂I³⁵Cl and ¹⁵N₂I³⁷Cl of a complex formed between dinitrogen and iodine monochloride were observed by pulsed-jet, Fourier-transform microwave spectroscopy. The spectra were interpreted on the basis of a linear equilibrium geometry with the weak bond formed between N and I. The spectroscopic constants B₀, D_J, χ_aa(I), χ_aa(Cl) and M_bb(I) were determined for each isotopomer and various models for the complex were employed to yield the distance r(NI)=3.180(2)Å, the intermolecular stretching force constant k_σ=5.37(3) Nm⁻¹, and the inter- and intramolecular electronic transfers δ_i=0.004(3) and δ_p(Cl)=0.018(2).     

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N₂O₄ solutions in organic solvents have been recorded. The frequencies ofv ₁,v ₂, andv ₃ bands of N₂O₄ increase with increasing solvent electron-donor properties. Especially large changes ofv ₃ N-N stretching band have been observed (254.5 cm^–1 in n-hexane, 276.5 cm^–1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N₂O₄ and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N₂O₄ in agreement with the results of Raman study.     

Spectroscopic studies of charge transfer complexes of meso‐tetra‐p‐tolylporphyrin and its zinc complex with some aromatic nitro acceptors in different organic solvents

The charge transfer complex (CTC) formation of 5,10,15,20‐tetra(p‐tolyl)porphyrin (TTP) and zinc 5,10,15,20‐tetra(p‐tolyl)porphyrin with some aromatic nitro acceptors such as 2,4,6‐trinitrophenol (picric acid), 3,5‐dinitrosalicylic acid, 3,5‐dinitrobenzoic acid (DNB) and 2,4‐dinitrophenol (DNP) was studied spectrophotometrically in different organic solvents at different temperatures. The spectrophotometric titration, Job's and straight line methods indicated the formation of 1:1 CTCs. The values of the equilibrium constant (K_CT) and molar extinction coefficient (ε_CT) were calculated for each complex. The ionization potential of the donors and the dissociation energy of the charge transfer excited state for the CTC in different solvents was also determined and was found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the electron affinity of the acceptors and the nature of the solvent. No CT band was observed between Zn‐TTP as donor and DNP or DNB as acceptors in various organic solvents at different temperature. Bimolecular reactions between singlet excited TTP (¹TTP*) and the acceptors were investigated in solvents with various polarities. A new emission band was observed. The fluorescence intensity of the donor band decreased with increasing the concentration of the acceptor accompanied by an increase in the intensity of the new emission. The new emission of the CTCs can be interpreted as a CT excited complex (exciplex). Copyright © 2007 John Wiley & Sons, Ltd.     

Mechanism of formation of YBa2Cu4O8 superconductor in the sol-gel synthesis

It was shown that a single phase YBa₂Cu₄O₈ (124-phase) could be formed from gels at 1 atm oxygen pressure, and the mechanism of its formation was elucidated. It was found that there are two key routes for the sol-gel formation of the 124-phase, one involving the tetragonal YBa₂Cu₃O _y with a low concentration of oxygen defects (tetra-I phase) and the other involving the Ba₂Cu₃O_5.9 as important intermediates of the 124-phase. The rapid formation of these intermediate compounds from the gel was attributed to the small particle size of the oxides and carbonates precipitating at the initial stage of heating. It was thought that the small particles characteristic of sol-gel processing lead to the rapid formation of the intermediate compounds and subsequent precipitation of the 124-phase.     

Reactions of co-ordinated ligands: Kinetics and mechanisms in the charge transfer interaction between dichloro or diaquo triethylene tetramine Co(III) and ferrocyanide

The cherry red-coloured solid state product obtained by the reaction ofcis-σ diaquo Co (III) triethylene tetramine with ferrocyanide was examined by thermogravimetric, infrared and M?ssbauer techniques. Its electronic spectrum in aqueous medium was interpreted to consist of charge transfer IT transition at 440 nm and a ligand field transition around 330 nm. The kinetics of formation of this 1:1 product in solution was also studied.     

Ab initio Calculation of the charge distribution and the ligand field splitting in the tetrahedral halo complexes CuCl 4 2− 4 and NiCl 4 2−

The charge distribution and the ligand field splitting in the tetrachloro complexes CuCl ₄ ^2– and NiCl ₄ ^2– have been investigated by means of the restricted Hartree-Fock method. A rather large basis set of contracted Gaussian type orbitals has been employed. The charge distributions have been analysed by means of Mulliken population analyses. The ligand field splitting 10Dq has been compared with literature results known for the octahedral cluster NiF ₆ ^4– occurring in KNiF₃. A detailed analysis has been carried out for CuCl ₄ ^2– . From calculations on a selected number of states of NiCl ₄ ^2– the Racah parameters B and C have been obtained.     

Kinetic and equilibrium study of the deprotonation of 4-nitrophenyl[bis(ethylsulphonyl)]methane by organic bases in acetonitrile in the presence of common cation BH<Superscript>+</Superscript> and tetrabutylammonium perchlorate

The results of kinetic and equilibrium experiments with the set of reaction of proton abstraction from 4-nitrophenyl[bis(ethylsulphonyl)]methane in acetonitrile are reported. Two strong organic bases are used: 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). The rates of proton transfer reaction have been measured by T-jump method in the presence of perchlorate of the appropriate base as a common cation BH⁺ and supporting electrolyte-tetrabutylammonium perchlorate (TBAP) in the temperature range between 20–40°C are: k _H =1.32×10⁷−2.00×10⁷ and 2.82×10⁷−4.84×10⁷ dm ³mol⁻¹s⁻¹ for MTBD and TBD respectively. The enthalpies of activation ΔH _MTBD ^≠ =13.5 and ΔH _TBD ^≠ =18.1 kJmol⁻¹. The entropies of activation are negative: ΔS _MTBD ^≠ =−62.3 and ΔS _TBD ^≠ =−40.3 Jmol⁻¹K⁻¹. The change of the absorbance of the anion of 4-nitrophenyl[bis9ethylsulphonyl)]methane at the temperature 25°C in the presence of common cation BH⁺ gives the equilibrium constants K=705 and 906 M⁻¹ for MTBD and TBD respectively. Kinetic and equilibrium results are discussed. The possible mechanism of proton transfer reaction between 4-nitrophenyl[bis(ethylsulphonyl)]methane and cyclic organic bases: MTBD and TBD in acetonitrile is proposed.     

Topological analysis of the charge density response of a Ni4 cluster to a probe H2 molecule

Local density self-consistent field (SCF) discrete variationalX calculations are performed on a Ni₄ tetrahedron interacting with a probe H₂ molecule in special geometries. Optimized basis functions generated from the spherically averaged SCF potential are used. Topological charge-density analyses and binding energy calculations are used to study a portion of the energy surface for the approach of the H₂ molecule toward the Ni₄ tetrahedron. The effect of the H₂ molecule on Ni-Ni, Ni-H bonds and changes in the H-H covalent bond are investigated with the help of the field and various data at its critical points. The qualitative relationship between these data and the calculated binding energies is exploited.     

Calorimetric investigations of the solvent effect on complex formation between pyridine derivatives and molecular iodine

The heats of solution of isoquinoline and 2,4-lutidine and heats of 11 complex formation with molecular iodine inn-hexane, cyclohexane, CCl₄, benzene, and chlorobenzene have been determined by the calorimetric method. The heats of transfer of the donor and donor-acceptor complex from nonsolvating medium (n-hexane) to the particular solvent were calculated and discussed in terms of donor and solvent properties and solute-solute-solvent interactions.Presented at the IV International Symposium on Solute-Solute-Solvent Interactions, Vienna, September 11–16, 1978, pp. 152–154.     

Selective O-acylation of unprotected N-benzylserine methyl ester and O,N-acyl transfer in the formation of cyclo[Asp-Ser] diketopiperazines

The synthesis of two diastereomeric cyclo[Asp-N-Bn-Ser] diketopiperazines (2a and 2b) was investigated. Initial formation of the Boc-aspartyl-N-benzyl serine isopeptide methyl esters (4a and 4b) was observed, which derive from the selective O-acylation of unprotected (S)- or (R)-N-benzylserine. This unexpected O-acylation is preferred over the formation of the tertiary amide and the resulting ester bond is stable in solution to O,N-acyl transfer. The O,N-acyl migration is then triggered by cleavage of the Boc protecting group and treatment with base, which also promotes immediate cyclization to the diketopiperazines.