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91.
核磁共振碳谱的研究:烷烃化学位移和CSS与分子距边矢量λ 总被引:2,自引:1,他引:1
系统研究了核磁共振碳谱及其化学位移规律性.提出了一种新的分子图论参数:分子距离一边数矢量(λ或MDE矢量),并发现它与烷烃的13C NMR有良好的相关性。 相似文献
92.
Jean-Luc Pirat Michel Carteron Annie-Francoise Maggio Stephanie Bot Henri-Jean Cristau 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):609-612
A new synthesis of 1,3,2λ5-dioxaphospholanes was realized by direct reaction of dibromotriphenylphosphorane with 1,2-diols. Ring opening studies were performed with or without electrophilic activation (Lewis acids or hydrogen bonding) in order to substitute selectively one of the hydroxy function. 相似文献
93.
Michaela GÖRg Ralph-Matthias Schoth Ildikó Székely Gerd-Volker Röschenthaler 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):667-670
Perfluoroalkenyl phosphonates were formed along with Me3SiF using CF3CF=CF2, CF3CH=CF2, F5SCF=CF2 or F5SCH=CF2 and silylated phosphites, (R1O)2POSiMe3 (R1=Et, SiMe3). This straightforward method could be extended to perfluorobutadienes CF2=C(RF)C(RF)=CF2 (RF F=F, CF3). The formation of CF3C(=O)P(=O)(OSiMe3)2 and further reactions to yield bisphosphonates will be described. Acetylphosphonates, R2C(=O)P(=O)(OSiMe3)2 (R2=CH3, CF3) reacted with the ketimine, CH3C(=NiPr)Ph to give α-hydroxy-γ-imino phosphonates. Trifluoroacetylphenol and 2,6-bis(trifluoracetyl)-4-methyl-phenol have been proven to be versatile precursors for α-and γ-hydroxy phosphonates. Intermediates in these reactions were found to be cyclic λ5σ5P species. 相似文献
94.
Herbert Hommer Barbara Gordillo 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):465-470
The exclusive synthesis of r -2-ethoxy- cis -4- cis -5-dimethyl-1,3,2- u 3 -dioxaphospholane ( cis - 1 ) is reported. The kinetic measurements of the epimerization of cis - 1 to trans - 1 were performed by 31 P NMR from 50 to 80;C in toluene. The energy of activation (E a ) of the epimerization process was calculated from Arrhenius plot. The thermodynamic parameters of the transition state led us to conclude that the activation barrier of the inversion at phosphorus is driven by the enthalpy and by a large and negative entropy of activation. 相似文献
95.
A new homologous series of λ-shaped mesogenic azo esters with polar chloro- and nitro- substituents has been synthesised by attaching a rigid 2-chloro-4-nitrophenylazo group to a resorcinol moiety by a central azo linkage. Both phenolic hydroxyl groups are esterified by 4-n-alkoxybenzoyl groups. All the compounds synthesised have been characterised using a combination of elemental analysis and standard spectroscopic methods. The mesomorphic properties of the compounds have been determined by polarising optical microscopy and differential scanning calorimetry. The lower members of the series are non-mesogenic, the middle members exhibit a nematic mesophase, and higher members exhibit a smectic A mesophase. The effect of polar chloro-, nitro-, and long lateral aromatic substituents, on mesomorphism is discussed. 相似文献
96.
In this paper, we study radial operators in Toeplitz algebra on the weighted Bergman spaces over the polydisk by the(m, λ)-Berezin transform and find that a radial operator can be approximated in norm by Toeplitz operators without any conditions. We prove that the compactness of a radial operator is equivalent to the property of vanishing of its(0, λ)-Berezin transform on the boundary. In addition, we show that an operator S is radial if and only if its(m, λ)-Berezin transform is a separately radial function. 相似文献
97.
98.
研究形如div A(x,u(x))=0的A-调和方程,证明其弱解满足局部Arλ3(λ1,λ2,Ω)-权Caccioppoli型不等式,这可看作A-调和方程相应结果的推广.最后给出上述结果在拟正则映射中的应用. 相似文献
99.
通过对线性的目标函数在线性的约束条件下的极值问题的分析,得到这类极值问题一般是不能用拉格朗日乘数法求解.通过用基础解系的方法进行求解这类问题,实例表明,这种方法是可行有效的. 相似文献
100.
The chiral macrobicyclic tri-λ5-phosphazenes formed by tripod-tripod coupling of tris(3-azidobenzyl)amines and 1,1,1-tris[(diphenylphosphino)methyl]methanes present helical topologies as a result of combining two propeller-shaped tripodal fragments with the same sense of twist. The introduction of a series of Rpiv substituents of increasing size at the pivotal carbon of the lower tert-butane fragment Rpiv-C(CH2PPh2)3 causes a gradual decrease of the helicity in the lower propeller. This phenomenon is revealed in their CDCl3 solution NMR spectra, and the activation energies for the racemization process of the tri-λ5-phosphazenes were calculated by coalescence VT-NMR experiments. 相似文献