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31.
The synthesis, IR, 1H NMR and UV spectra of optically active square pyramidal cyclopentadienyldicarbonyl-molybdenum and -tungsten complexes with Schiff bases, derived from methyl-substituted pyridine carbaldehyde(2) and S-(—)-α-methylbenzylamine, are described. The epimerisation of these complexes, measured polarimetrically at 75–97°C in DMF, follows a 1st order rate law and represents a regular pentatopal skeletal rearrangement. The inductive effect of a methyl group in the para position of a pyridine ring leads to a retardation of the epimerisation compared to unsubstituted complexes. The rate constants decrease even more if an ortho methyl group is introduced into the pyridine system, since additional steric effects are introduced. If the metal complex contains a 4,6-dimethyl-substituted Schiff base as a chelating ligand, the contributions of a 4- and a 6-methyl group are additive. A benzene ring fused to the 5,6-positions of the pyridine system also leads to stabilisation of the configuration. 相似文献
32.
Henri Magnin Firmin Rodriguez Marc Abadie Franois Schu 《Journal of polymer science. Part A, Polymer chemistry》1977,15(4):875-895
A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH2CH2)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)2 as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization. 相似文献
33.
Jun-ichi Azuma Nam-Hun Kim Laurent Heux Roger Vuong Henri Chanzy 《Cellulose (London, England)》2000,7(1):3-19
The cellulose system of the viscous fibrous cellulosic polysaccharide (viscan) in the viscin tissue of the European mistletoe, Viscum album L., was analyzed by chemical and physicochemical techniques including sugar analysis, optical and transmission electron microscopy, X-ray and electron diffraction together with solid state CP/MAS 13C-NMR spectroscopy. The results confirmed that in the elongated thin viscin cells, the cellulose microfibrils (having a diameter of around 3 nm) were tightly coiled with their axes perpendicular to the long axis of the cell. Upon stretching these cells became deformed by more than a hundred fold. In such a deformation, the cellulose microfibrils became unwound to be perfectly aligned along the stretching direction. Based on solid-state CP/MAS 13C-NMR spectroscopic analysis of the viscin tissue, it was found that its cellulose consisted of I and I polymorphs in the ratio 1:1. 相似文献
34.
The reaction of PhSeCl and N-PSP with homogeranic acid () or homoneric acid () affords butanolides in a stereospecific way. Despite the large number of cyclic cases studied in the literature such acyclic systems were remained largely unexplored. PhSe+ was unable to realize polycyclization. 相似文献
35.
During electrolysis of molten KF-2HF, strongly adherent fluorine bubbles are generated at the surface of carbon anode. The current was passing even if the horizontal anode was fully covered with gas film. The formation and growth of gas bubbles were studied by transient electrochemical techniques. It was observed that the fluorine bubbles do not have the spherical cap shape predicted by the classical theory. The curvature radius of the interface profile is not constant, the edge of the bubble being flat with a contact angle close to zero. The results are interpreted in the frame of a model which takes into account the predominant role of the interfacial properties. 相似文献
36.
Elizabeth Dinand Michel Vignon Henri Chanzy Laurent Heux 《Cellulose (London, England)》2002,9(1):7-18
The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with 13C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains. 相似文献
37.
The amine substituted phosphines (C6H5)2PN(H)CH2CH3 and (C6H5)2PN(H)CH2C6H5 react with C5H5Fe(CO)2CH(C6H5) (OCH3) photolytically to give moderate yields of the four-membered chelate ring complexes C5H5H (C6H5)] and C5H5H(C6H5)], respectively. Photolysis of C5H5Fe(CO)2CH(C6H5) (OCH3) in the presence of (S)-(?)-diphenyl(1-phenylethylamino)phosphine leads to the isolation of C5H5Fe(CO)[(C6H5)2PNC(CH3) (C6H5)]CH2C6H5 which is proposed to arise from a formally 1,3-hydrogen shift rearrangement of an intermediate four-membered chelate ring complex. 相似文献
38.
Reaction of the 1-substituted-3-cyano-isothioureas 6 with hydroxylamine gave mixtures of the 5-amino-3-substituted-amino-1,2,4-oxadiazoles 1 and the isomeric 3-amino-5-substituted-amino-1,2,4-oxadiazoles 8 in which 1 usually predominated. The structural assignment of these products is discussed. In a second method, the 2-hydroxy-1-methyl-1-phenyl-guanidine 15 was converted to the corresponding 3-disubstituted-amino-5-trichloromethyl-1,2,4-oxadiazole 16 , a precursor to the 5-amino derivatives 17 by nucleophilic displacement of the trichloromethyl group. 相似文献
39.