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21.
A deuteron magnetic resonance and infrared study of the water molecules in lithium formate monohydrate, LiHCOO · H2O, has been made. The quadrupole coupling constants (e2qQ/h) and asymmetry parameters (η) were found to be 198.7±0.4 and 231.3±0.6 kHz, and 0.060±0.005 and 0.097±0.003, respectively, at 25 ° C.An interpretation is given of the infrared spectra in the OH-stretching region in terms of intra- and intermolecular couplings of the water molecules. It is found that the water molecules are vibrationally distorted by their environments such that the OH-stretching modes consist of independent stretchings of the two O-H bonds. 相似文献
22.
23.
The base alkylation of 2,3-dimercapto-1-propanol with alkyl halides leads in good yield to 2,3-bis(alkylthio)-1-propanol and dialkyl sulfide. The reaction of 2,3-bis(alkylthio)-1-propanol with catalytic concentrated sulfuric acid proceeds with rearrangement to give 1,2,3-tris(alkylthio)propane and dialkyl disulfide. The rearrangement reaction takes place through a common intermediate thiaranium intermediate 8. 相似文献
24.
The first total synthesis of marine bioactive cyclic heptapeptide Leucamide A has been accomplished, including a simple method for construction of the 4,2-bisheterocycle tandem pair substructure that employs a DAST-mediated cyclization of beta-hydroxy amide and final HBTU-promoted ring closing. 相似文献
25.
The electric field gradient (EFG) tensors at the deuterons in the water molecules in BeSO4 · 4D2O at 25°C are reported. The quadrupole coupling constants (e2Q/h) and asymmetry parameters (η) for the two independent deuterons are 181.1(4) and 194.8(3) kHz, and 0.226(4) and 0.123(3), respectively. The EFG tensor corresponding to the smallest e2qQ/h is considerably distorted by the beryllium ion, which causes a high η value as well as a deviation of the y-principal axis by 21.8(6)° from the normal to the water molecule plane. A redetermination of the EFG tensors at the deuterons in the water molecule in Li2SO4 · D2O at 25°C and ?110°C is also reported. The e2Q/h and η values for the two deuterons are 236.6(1.2) and 239.8(1.1) kHz, and 0.091(8) and 0.126(7), respectively, at ?110°C. The corresponding e2qQ/h and η values for the averaged EFG tensor at 25°C are 125.8(1.1) kHz and 0.813(13), respectively. The results are in good agreement with those from the pioneer work by Ketudat and Pound, 20 years ago on the same compound. 相似文献
26.
Zusammenfassung Bei der Umsetzung von Methylphenylacetat mit Dialkylamiden der Zimtsäure in Gegenwart von NaNH2 wurden Amidester der (±)-erythro-2,3-Diphenylglutarsäure hergestellt. Die Konfiguration der erhaltenen Verbindungen wurde durch Hydrolyse mit HCl (1:1) zu der entsprechenden Säure und im Falle der Umsetzung mit dem Zimtsäuredimethylamid durch eine mehrstufige Synthese aus demerythro-Säurenitril-ester festgestellt. Es wurden auch Bedingungen gefunden, unter welchen nur die Estergruppe hydrolysiert werden kann, wobei Mono-dimethylamid entsteht, das mit CH2N2 den Ausgangs-Amidester liefert. 相似文献
27.
New 2D graphical representation of DNA sequences 总被引:5,自引:0,他引:5
We consider a 2D graphical representations of DNA sequences, which avoids loss of information associated with crossing and overlapping of the corresponding curve. We outline an approach, which is based on the construction of a three-component vector whose components are the normalized leading eigenvalues of the L/L matrices associated with DNA. The examination of similarities/dissimilarities among the coding sequences of the first exon of beta-globin gene of different species illustrates the utility of the approach. 相似文献
28.
Yang Nan Subhash P. Upadhyaya Wei Xu Kathrine E. Hughes William J. Dunn Ludwig Bauer Hemendra N. Bhargava George A. Doss 《Journal of heterocyclic chemistry》1996,33(2):399-407
A number of (E)-7-arylidenenaltrexones were synthesized by azeotropic distillation of water from a benzene solution of naltrexone and an aromatic aldehyde (benzaldehyde, 4-chloro- and 4-fluorobenzaldehyde, 3-and 4-pyridinecarboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde) using piperidine as a catalyst. In addition, (E)-7-benzylidenenaloxone was prepared by the previously published Claisen-Schmidt condensation using sodium hydroxide in methanol. The stereochemistry of these arylidene derivatives 3–9 was determined to be (E) by means of nuclear Overhauser enhancement experiments. The 13C nmr spectra of (E)- 3–9 are recorded in deuteriochloroform and those of the hydrochlorides in deuteriodimethyl sulfoxide. 相似文献
29.
Analysing experimentally determined P, ?, T data of N2, ethylene, propene, CO2 and Xe by a new mathematical technique, we present evidence that their isothermal pressure-density dependence exhibits behaviour characteristic of a Riemann-Hugoniot catastrophe, in analogy to a van der Waals gas for above and sub critical isotherms. 相似文献
30.
Nan Zhou 《Mikrochimica acta》1991,105(4-6):159-162
Proposed in this paper is an improved method for removal of tin as the matrix element by volatilization in an anhydrous medium as mixed halides of different composition. Any one of them boils at a lower temperature than SnBr4. This ternary system enhances the eventual recombination of temporarily dissociated species to volatile ones, thus making the process quicker and more efficient. The presence of 2 mg of Pb(II) suffices to prevent Bi(III) from loss due to volatilization. 相似文献