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61.
W. Weissensteiner 《Monatshefte für Chemie / Chemical Monthly》1992,123(12):1135-1147
Summary Ground state structures and conformational interconversion mechanisms of 25 diaryl compoundsAr
2
Z (Z=CH2, CHR, CH(OH), P-CH3) were analyzed. For tetra(ortho-alkyl)substituted diaryls the cogwheeling mechanism was found as the threshold mechanism. A shift from the cogwheeling mechanism to interconversions via 2-ring flips is found in di(ortho-alkyl)substituted compounds. The ground state structures and interconversion mechanisms of diarylmethylphosphines are very similar to those of the related 1,1-diarylethanes. The interconversion barrier for correlated conrotation of the aryl rings in di(tert-butylphenyl)methanol (20) was measured by low temperature NMR and is in excellent agreement with the calculated value for the 2-ring flipT2 (G (exp.)=48 kJ mol–1; G (calc.)=54 kJ mol–1).
Korrelierte Rotation von Arylringen in Diarylmethyl-, Diarylphosphin- und verwandten Fragmenten. Eine Untersuchung mit Hilfe der empirischen Kraftfeldmethode
Zusammenfassung Die Grundzustandskonformationen und die konformativen Interkonversions-mechanismen von 25 DiarylverbindungenAr 2 Z (Z=CH2, CHR, CH(OH), P-CH3) wurden analysiert. Für tetra(ortho-alkyl)substituierte Diaryle wurde der cogwheeling-Mechanismus als der Interkonversionsmechanismus niedrigster Energie ermittelt. In di(ortho-alkyl)substituierten Verbindungen werden nicht der cogwheeling-Mechanismus sondern 2-ring flips als Interkonversionsmechanismen gefunden. Die Grundzustände und Interkonversionsmechanismen für Diarylmethylphosphine sind sehr ähnlich jenen der verwandten 1,1-Diarylethane. Die Interkonversionsbarriere für die korrelierte Bewegung der Arylringe von Di(tert-butylphenyl)methanol (20) wurde mittels Tieftemperatur-NMR-Spektroskopie ermittelt und ist in sehr guter Übereinstimmung mit dem berechneten Wert für den 2-Ring flipT2 (G (exp.)=48 kJ mol–1; G (calc.)=54 kJ mol–1).相似文献
62.
On the plastic deformation of bulk syndiotactic polypropylene 总被引:1,自引:0,他引:1
The plastic deformation of syndiotactic polypropylene (sPP) bulk samples has been investigated. A structural comparison of
the initial states before and after plastic deformation by necking is carried out by X-ray diffraction observations. Independent
of the initial states (amorphous, semi-crystalline with different crystal phases), only the planar all-trans crystal form of sPP is present in the deformed samples after necking. Form these results, molecular mechanisms of the plastic
deformation in the neck zone of semi-crystalline polymers will be discussed.
Received: 11 February 1997 Accepted: 15 August 1997 相似文献
63.
Istvan Bakk Dietrich Gudat Stefan Hp Martin Nieger Lszl Nyulaszi Lszl Szarvas 《无机化学与普通化学杂志》2005,631(1):47-54
Reactions of the phosphonio‐benzophospholide π‐complexes 3a, b[Cr] with [M(CO)5(olefin)] or of the σ‐complexes 2a, b[M] (M = Cr, Mo, W) with [M(CO)3(aren)] lead to the first binuclear complexes 4a, b[CrM] featuring phosphonoio‐benzophospholides as μ‐bridging 8e‐donor ligands to two group 6 metal atoms. The constitution of the products was determined by spectroscopic and X‐ray diffraction studies. Mixed complexes with both group 6 and 7 metals were not accessible. Mechanistic studies showed that the reactions follow a complicated mechanism whose single steps may involve transfer of either M(CO)n fragments or single CO ligands between complexes; the latter are associated with a σ/π‐coordination isomerization of the benzophospholide unit. Competition between both reaction channels can lead to the formation of product mixtures whose composition is controlled by the relative thermodynamic stabilities of the products. Computational studies suggest that in the more stable isomer of heterobimetallic complexes 4a, b[MM′] end‐on coordination to the heavier and side‐on coordination to the lighter metal atom is preferred. 相似文献
64.
V. I. Minkin I. E. Mikhailov G. A. Dushenko O. E. Kompan A. Zschunke 《Russian Chemical Bulletin》1998,47(5):884-894
The kinetics and mechanism of circumambulatory rearrangements of N-centered (NCS) and S-centered (SPh, SC3Ph3, SC(OEt)=S) groups in corresponding derivatives of 1,2,3-triphenylcyclopropene and cycloheptatriene were studied by dynamic1H and13C NMR spectroscopy. Migrations of the isothiocyanate group occur by the dissociation-recombination mechanism with intermediate formation of a tight ionic pair. Migrations of the phenylthio group around the perimeter of cyclopropene and cycloheptatriene rings occur by the 1,2-shift mechanism. It was found that rearrangements of theO-ethyl dithiocarbonate group inS-(1,2,3-triphenylcyclopropen-3-yl)-O-ethyl dithiocarbonate occur by the 3,3-sigmatropic shift mechanism. The molecular and crystal structure ofO-ethylS-(1,2,3-triphenylcyclopropen-3-yl) dithiocarbonate was studied by X-ray analysis. 相似文献
65.
Shi-Rong Hu Jia-Ming Liu Tian-Long Yang Hai-Zhu Liu Jun-Li Huang Qing-Wei Lin Guo-Hui Zhu Xiao-Mei Huang 《Mikrochimica acta》2005,152(1-2):53-59
Luminescent nanoparticles of silicon dioxide (SiO2) containing fluorescein isothiocyanate (FITC) with a particle size of 20 nm were synthesized using the Sol–Gel method (abbreviated
FITC–SiO2). FITC–SiO2 nanoparticles whose surfaces are modified (FITC–SiO2–S–CH2COOH) can emit strong and stable solid substrate room temperature phosphorescence (SS-RTP) on acetyl cellulose membranes.
When the original color-producing agent (R) in the enzyme-linked immunosorbent assay (ELISA) kits for determination of alpha-fetoprotein
(AFP) was substituted with (FITC–SiO2–S–CH2COOH), the system maintained good FITC–SiO2 phosphorescence properties. Furthermore, the phosphorescence intensity enhanced markedly after the ELISA reaction. The relationship
between the phosphorescence intensity and the content of AFP obeyed Beer’s law. Based on the facts stated above, a new method
for the determination of human AFP by SS-RTP-ELISA (using the luminescent nanoparticle as marker) was established. The linear
range of this method is 0.040–16.0 pg of human AFP per spot (sample volume: 0.40 μL spot−1, corresponding concentration: 0.10–40.0 ng mL−1). The regression equation of the working curve is ΔIp = −6.289+18.075 mAFP (pg spot−1) (r = 0.9960, n = 6). The detection limit (LD) of this method calculated by 3 Sb/k is 6.7 fg spot−1 (corresponding concentration: 17 ng L−1). Compared to the ELISA method using a traditional color-producing agent, the new method exhibited a 34.8 times higher sensitivity
and a wider linear range. The method has been successfully applied to the determination of human AFP in serum. 相似文献
66.
A study of the mechanisms involved in the separation of metal ions with a mixed-bed stationary phase
Summary The optimization of chromatographic methods for the determination of metal species require an understanding of the mechanisms
involved. In this work, the separation of Cd, Co, Cu, Fe(II/III), Mn, Pb and Zn using a mixed bed column (IonPac CS5A) and
a cation-exchange column (IonPac CS2) is studied as a function of mobile phase composition. The type and concentration of
complexing agent and of ionic strength modificators were evaluated. The charge of analytes were calculated using the classical
ion exchange approach to highlight the effect of eluent composition on retention. The comparative study enabled us to identify
an optimal eluent composition for the separation of the nine metal species. 相似文献
67.
Maurí cio Braga de Araú jo Nelson Moreira Pinhal Ney Vernon Vugman 《Radiation Physics and Chemistry》2002,64(5-6):389-393
The kinetics of oxidized and reduced Ni2+ complexes produced by X-ray irradiation on single crystals of NaCl doped with [Ni(CN)4]2− is studied by Electron Paramagnetic Resonance at room temperature. The interdependent generation of these two complexes is attributed to migration of the charge compensating vacancy from the reduced to the oxidized complex in a reversible reaction. At higher X-ray doses, there is a predominant formation of the reduced complex. 相似文献
68.
H. -J. Sue E. I. Garcia Meitin D. M. Pickelman C. J. Bott 《Colloid and polymer science》1996,274(4):342-349
The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT
g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed. 相似文献
69.
Unimolecular fragmentation patterns of the molecular ions of selected lactams and sultams bearing alkoxymethyl group at the nitrogen atom were studied. The main common fragmentation reaction observed for all compounds studied in this work is the elimination of an aldehyde molecule. This reaction is considered to proceed via two different mechanisms. For lactams, hydrogen rearrangement within an alkoxymethyl group is observed, which leads to the appropriate N-methyl derivatives. For sultams, transfer of the methyl group to the nitrogen and oxygen atoms, proceeding through an ion-neutral complex, dominates. Another important fragmentation channel characteristic exclusively for lactams is the loss of an alkyl radical. This process takes place within the N-alkoxymethyl moiety, yielding the appropriate protonated ion of N-formyllactams. This process is accompanied by relatively high kinetic energy release. 相似文献
70.