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1.
R. Markovi M. Baranac N. Jurani S. Macura I. Ceki D. Mini 《Journal of Molecular Structure》2006,800(1-3):85-92
The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic 1H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl3 at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG# 98.5 kJ/mol (at 298 K). The variable-temperature 1H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d6, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The 13C NMR ΔδC(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH2CH2Ph. The decrease of the ΔδC(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds. 相似文献
2.
Hua-Ming Zhang Shao-Yi Wu Yue-Xia Hu Xue-Feng Wang Pei Xu 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,73(5):879-883
The local angular distortions and the spin-Hamiltonian parameters (the g factors and the hyperfine parameters) for Ni+ in ABS2 (ACu, Ag; BAl, Ga) ternary sulfides are theoretically investigated from the perturbation formulas of these parameters for 3d9 ions in a tetragonally distorted tetrahedron. In view of the strong covalency of such systems, the ligand orbital and spin–orbit coupling contributions are taken into account using the cluster approach. The local impurity-ligand bond angles in the Ni+ centers are found to be about 1.4–4.5° smaller than those of the host monovalent A sites in the pure crystals, due to size mismatching substitution. As a result, the ligand tetrahedra exhibit slight elongation in CuBS2:Ni+ and slight compression in AgGaS2:Ni+. The calculated spin-Hamiltonian parameters, optical transitions and the relative intensity ratios show reasonable agreement with the experimental data. 相似文献
3.
J. Pajak G. Maes W.M. De Borggraeve N. Boens A. Filarowski 《Journal of Molecular Structure》2008,880(1-3):86
The paper presents the conformational, vibrational and hydrogen bond characteristics of 5-methyl-3-nitro-2-hydroxyacetophenone studied with the combined matrix-isolation FT-IR spectroscopic and theoretical (DFT/B3LYP/6-31++G**) technique. Theoretical calculations predict three stable conformations of the studied compound. Only two of these conformations could be identified experimentally using the matrix-isolation FT-IR technique. The conformation with the intramolecular hydrogen bond OH…ON has been found to be more stable than the conformation with the OH…OC type of hydrogen bond by 7.28 kJ/mol. The complete assignment of the experimental spectra could be performed based on the theoretical calculations including the normal coordinate analysis and isotopic substitution. 相似文献
4.
M. Umadevi R. Regi Poornima 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,73(5):815-822
FTIR spectra of propionic acid (PA), N,N-dimethyl formamide (DMF) and its binary mixtures with varying molefractions of the PA were recorded in the region 500–3500 cm−1, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), δ(OC–N) and νas(CN) of DMF, ν(CO) and ν(CO) of PA have been explained in terms of the hydrogen bonding interactions between DMF and PA and dipole–dipole interaction. The intrinsic bandwidth for the vibrational modes νas(CN) and ν(CO) has been elucidated using Bondarev and Mardaeva model. 相似文献
5.
Raman spectra of some solid and molten PCl5–ZrCl4 mixtures have been recorded. ZrCl6
2– complex ions accompanied by at least one more chlorozirconate species are present in the solid as well as in the melt. The newRaman frequencies are attributed to ZrCl5
–, which fundamentals are given and assignment is proposed to be analogous to TiCl5
–. The presence of ZrCl6
2– and ZrCl5
– can be explained by the equilibrium ZrCl6
2–+PCl4
+ZrCl5
–+PCl5. 相似文献
6.
Yukiteru Katsumoto Takeyuki Tanaka Yukihiro Ozaki Shinzo Hosoi 《Vibrational Spectroscopy》2009,51(1):119
The concentration dependence of the CO stretching (νCO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl4 has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the νCO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the νCO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the νCO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl4 solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the νCO band observed in a highly diluted CCl4 solution (≤0.023 M) indicate that the solvation effect of CCl4 is more complicated than those of cyclohexane and n-hexane. The analyses of the νCO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution. 相似文献
7.
A precise, reliable, sensitive, and selective method for the determination of titanium(IV) is described. Titanium(IV) reacts withN
1-hydroxy-N
1,N
2-diphenylbenzamidine (HDPBA) and thiocyanate to form an orange-coloured mixed-ligand complex of stoichiometry 112 (Ti SCN– HDPBA). The complex is quantitatively extractable into toluene from 0.05–0.15M hydrochloric acid. The spectrum of the complex exhibits an absorption maximum at 400 nm with a molar absorptivity of 20000M
–1 cm–1 and the coloured system obeys Beer's law in the concentration range 0.20–3.0 gml–1 titanium. The effects of foreign ions and of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of titanium. The precision of the method has been evaluated and the relative standard deviation has been found to be 0.53%. The method has been successfully applied to the determination of titanium in synthetic matrices corresponding to titanium-containing ores, minerals, and alloys. 相似文献
8.
The reaction of the heteroleptic Nd(III) iodide, [Nd(L′)(N″)(μ-I)] with the potassium salts of primary aryl amides [KN(H)Ar′] or [KN(H)Ar*] affords heteroleptic, structurally characterised, low-coordinate neodymium amides [Nd(L′)(N″)(N(H)Ar′)] and [Nd(L′)(N″)(N(H)Ar*)] cleanly (L′ = t-BuNCH2CH2[C{NC(SiMe3)CHNt-Bu}], N″ = N(SiMe3)2, Ar′ = 2,6-Dipp2C6H3, Dipp = 2,6-Pri2C6H3, Ar* = 2,6-(2,4,6-Pri3C6H2)2C6H3). The potassium terphenyl primary amide [KN(H)Ar*] is readily prepared and isolated, and structurally characterised. Treatment of these primary amide-containing compounds with alkali metal alkyl salts results in ligand exchange to give alkali metal primary amides and intractable heteroleptic Nd(III) alkyl compounds of the form [Nd(L′)(N″)(R)] (R = CH2SiMe3, Me). Attempted deprotonation of the Nd-bound primary amide in [Nd(L′)(N″)(N(H)Ar*)] with the less nucleophilic phosphazene superbase ButNP{NP(NMe2)3}3 resulted in indiscriminate deprotonations of peripheral ligand CH groups. 相似文献
9.
Delphine Moraleda Douniazad El Abed Hlne Pellissier Maurice Santelli 《Journal of Molecular Structure》2006,760(1-3):113-119
A linear relationship between the half-wave reduction potentials of α,β-unsaturated carbonyl compounds R–CHCH–COX and the Hammett σp values of R and X is proposed: E1/2=−1.341σp(X)σp(R)+1.123σp(X)+1.746σp(R)−1.694. A linear relationship is also observed for the LUMO's energy values, the absolute chemical hardness η, the chemical potential μ, the electrophilicity power ω, or the polarisation of the ethylenic double bond with the Hammett σp values of R and X. 相似文献
10.
Peter Rapta Andrea Vargov Júlia Polovkov Anton Gatial Ladislav Omelka Petr Majzlík Martin Breza 《Polymer Degradation and Stability》2009,94(9):1457-1466
Electrochemical and spectroscopic (EPR, UV–Vis, IR) studies of the aromatic secondary amines N,N′-diphenyl-1,4-phenylenediamine (DPPD), N-phenyl-N′-isopropyl-p-phenylene diamine (IPPD), N-phenyl-N′-(α-methylbenzyl)-p-phenylenediamine (SPPD) and N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), which represent the most important group of antioxidants used in the rubber industry, are presented. During oxidation, all the compounds show reversible redox couples in acetonitrile/0.1 M TBABF4. The first oxidation potential depends substantially on the R substituent at the –N′H– moiety. Very similar UV–VIS spectra of monocation radicals and dications for all the compounds were observed by applying anodic oxidation as well as oxidation by tert-butyl hydroperoxide both in air and in inert atmosphere. The samples with N′-bonded aliphatic carbon in the molecule (e.g. IPPD) heated in air undergo consecutive chemical reactions leading to the formation of –N′C– group. By the use of RO2 radicals only very low concentration of nitroxide radicals was obtained. Very high concentration of nitroxide radicals was achieved using 3-chloroperbenzoic acid. In the oxidation of investigated aromatic secondary amines with powder PbO2 no EPR spectra were observed and UV–Vis and IR studies indicate the rapid formation of the final dehydrogenated oxidation product. 相似文献
11.
Siwei Bi Yuxia Liu Guang Chen Lisheng Zhang Min Sun Ping Li 《Journal of organometallic chemistry》2009,694(21):3456-3461
Selective formation of (η3-siloxyallyl)tungsten complexes by reaction of hydrido(hydrosilylene)tungsten complexes with α,β-unsaturated carbonyl compounds was reported experimentally. The mechanisms have been investigated by employing the model reaction of [Cp(CO)2(H)WSi(H)–{C(SiH3)3}] (R), derived from the original experimental complex Cp′(CO)2(H)WSi(H)–[C(SiMe3)3] (1a, Cp′ = Cp*; 1b, Cp′ = η5-C5Me4Et), with methyl vinyl ketone, under the aid of the density functional calculations at the b3lyp level of theory. It is theoretically predicted that the route involving migration of the hydride to silicon to afford a 16e intermediate [Cp(CO)2W–SiH2–{C(SiH3)3}] is inaccessible (route 2), supporting the proposition by experiments. Another route, via [2 + 4] cycloaddition followed by directly Si–H reductive elimination, is theoretically predicted to be accessible (route 1). In route 1, two possible paths with different attacking directions of the oxygen of methyl vinyl ketone at Si (WSi) are put forward. The attack at the Si atom from the hydride (H1) side of the plane W–Si–H1 in R is found to be preferred kinetically. The regioselectivity for formation of (η3-siloxyallyl)tungsten complexes, where only the exo-anti isomer was obtained, is discussed based on the consideration of thermodynamics and kinetics. 相似文献
12.
M. Krauze-Baranowska T. Baczek D. Głód R. Kaliszan E. Wollenweber 《Chromatographia》2004,60(1-2):9-15
Flavonoids present in the extracts from leaves of Pseudotsuga menziesii (Pinaceae), Ginkgo biloba (Ginkgoaceae) and Podocarpus dacrydioides (Podocarpaceae) were separated by use of the reversed phase HPLC method. The analysed compounds belong to different groups of flavonoids – biflavones (amentoflavone, bilobetin, 5–methoxybilobetin, podocarpusflavone A, sequoiaflavone, podocarpusflavone B, ginkgetin, isoginkgetin, sciadopitysin, kayaflavone, hinokiflavone, 2,3–dihydrosciadopitysin, 2,3–dihydroisoginkgetin), O–acylated flavonol glycosides (daglesiosides I, II, III, IV, trans–tiliroside, trans–ditiliroside), flavonol O–glycosides (astragalin, isoquercetin) and flavonol aglycones (kaempferol, quercetin, isorhamnetin). The conditions for flavonoid separation were optimized using various RP–18 columns. The chromatographic resolution was performed with isocratic or gradient elution – optimized by Drylab program or by traditional trial-and-error method, depending on the composition of flavonoid complex. 相似文献
13.
A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at various temperatures in two separate spectral ranges: 1780–1700 and 3100–2650 cm−1. The samples are studied in polycrystalline phase at room temperature, in isotropic liquid phase, and in polycrystalline phase after cooling from the isotropic liquid phase. The CO stretching mode of these triglycerides changes significantly according to the temperature: we observe three components, or an unresolved doublet, or a resolved doublet. The I(2845)/I(2880) ratios (in the C–H stretching spectral region) of the different saturated monoacid triglycerides vary also according to the temperature. The study of these two indicators (the CO stretching mode and the I(2845)/I(2880) ratio) has permitted us to determine the polymorphic forms of the studied triglycerides. 相似文献
14.
Harumi Sato Rumi Murakami Katsuhito Mori Yuriko Ando Isao Takahashi Isao Noda Yukihiro Ozaki 《Vibrational Spectroscopy》2009,51(1):132-135
Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm−1 due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH3 group of one helix and the CO group of another helix. 相似文献
15.
Strontium Sorption on Hematite at Elevated Temperatures 总被引:1,自引:0,他引:1
Karasyova ON Ivanova LI Lakshtanov LZ Lövgren L 《Journal of colloid and interface science》1999,220(2):419-428
Acid–base reactions and surface complexation of Sr(II) at the hematite/water interface have been studied by means of potentiometric titrations at three different temperatures: 25, 50, and 75°C. Equilibrium measurements were performed in 0.1 M NaCl. In the evaluation of equilibrium models for the acid–base reactions and complexation reactions in the three-component system H+ ---(FeOH)---Sr2+, the constant capacitance model was applied. During the titrations with Sr, aliquots of the suspension were sampled at in several points. The aqueous concentrations of Sr were analyzed by atomic absorption spectrometry. Treatment of data included tests for formation of both inner-sphere and outer-sphere complexes of different stoichiometric composition. The proposed equilibrium model consists of the following surface complexes of inner sphere type: FeOHSr2+ and FeOSrOH. Besides the stability constants for the surface complexes, the thermodynamic parameters ΔH and ΔS were evaluated. The combined effect of a decrease in pHpzc with increasing temperature and positive enthalpies of surface complex formation favors adsorption of Sr at elevated temperatures. 相似文献
16.
Treatment of a N-arylanilido-imine ligand [ortho-C6H4(NHAr)CHN]2CH2CH2 (Ar = 2,6-Me2C6H3) (LH2) with one equiv. of AlMe3 affords a monometallic complex [C6H4(NHAr)–CHN)]CH2CH2(C6H4(NAr)CHNAlMe2) (1). The monometallic complex 1 reacts with one equiv. of ZnEt2 to give a heterobimetallic complex [C6H4(NAr)–CHNZnEt]CH2CH2[C6H4(NAr)–CHNAlMe2] (2). Both complexes were characterized by 1H and 13C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner. 相似文献
17.
Ts. Kolev B.B. Koleva R. Nikolova R.W. Seidel H. Mayer-Figge M. Spiteller W.S. Sheldrick 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,73(5):929-935
Four different dimethyltin(IV) complexes of Schiff bases derived from 2-amino-3-hydroxypyridine and different substituted salicylaldehydes have been synthesized. The compounds, with the general formula [Me2Sn(2-OArCHNC5H3NO)], where Ar = –C6H3(5-CH3) [Me2SnL1], –C6H3(5-NO2) [Me2SnL2], –C6H2(3,5-Cl2) [Me2SnL3], and –C6H2(3,5-I2) [Me2SnL4], were characterized by IR, NMR (1H and 13C), mass spectroscopy and elemental analysis. Me2SnL3 was also characterized by X-ray diffraction analysis and shows a fivefold C2NO2 coordination with distorted square pyramidal geometry. H3C–Sn–CH3 angles in the complexes were calculated using Lockhart's equations with the 1J(117/119Sn–13C) and 2J(117/119Sn–1H) values (from the 1H-NMR and 13C-NMR spectra). The in vitro antibacterial and antifungal activities of dimethyltin(IV) complexes were also investigated. 相似文献
18.
Hua-Hong Zou Shu-Hua Zhang Ming-Hua Zeng Yan-Ling Zhou Hong Liang 《Journal of Molecular Structure》2008,885(1-3):50-55
A novel linear trimeric-based, Mn(II)–carboxylate chain well separated by long-linking flexible aliphatic tricarballylic acid ligands in a 3D coordination polymer [Mn3(C6H5O6)2(H2O)4]n (1, C6H5O6CH (COO−)(CH2COO−)2, TCA) exhibits low-dimensional antiferromagnetic order at 3.0 K. Such magnetic behavior is arises from the alternate Antiferro–Antiferro–Antiferro′ (J1 J1 J2) repeating interactions sequence, based on the nature of the binding modes of Mn(II)-carboxylate chain and the effect of interchains arrangement of 1. The reported carboxylate-bridged metal chain systems display a new structurally authenticated example of linear homometallic spin arranged antiferromagnet among metal carboxylates. 相似文献
19.
The solvent extraction of tin(IV) from chloride media withtris(2-ethylhexyl)phosphate is presented. Tin(IV) is extracted quantitatively from 2.75–3.20 mol dm–3 hydrochloric acid using 6.38–6.91 mol dm–3
tris(2-ethyl-hexyl)phosphate dissolved in toluene as an extractant. After back-extraction of tin(IV) with water from thetris(2-ethylhexyl)phosphate phase, it is estimated spectrophotometrically following complexation with pyrocatechol violet. The recommended range for determination of tin(IV) is 10–100 g. The probable extracted species is SnCl4·2TEHP. The method is applicable to the analysis of alloy samples with a detection limit of 0.4 g/ml (for 10 g of tin) and a relative standard deviation between 0.21–0.32%. 相似文献
20.
Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO2H2
LX
2, UO2H2
LX
2 and UO2(HL)2
X
2 [H2
L=N,N-propane-1,3-diylbis(salicylideneimine), H2
L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X
–=Cl–, Br–, I–, NO3
–, ClO4
–, and NCS–]. Because of marked spectral similrities with the structurally known Ca(H2
L) (NO3)2, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.
Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen
Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO2H2 LX 2, UO2H2 LX 2 und UO2(HL)2 X 2 [H2 L=N,N-Propan-1,3-diylbis(salicylidenimin), H2 L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X –=Cl–, Br–, I–, NO3 –, ClO4 – und NCS–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H2 L) (NO3)2 wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX – sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.相似文献