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1.
G. P. Jones B. A. Cornell E. Horn E. R. T. Tiekink 《Journal of chemical crystallography》1989,19(4):715-723
The crystal structures of dimethylsuccinate (DMS) and dimethyloxalate (DMO) have been determined to facilitate the determination of the C-13 chemical shielding tensors of the carbonyl carbon in esters. Crystals of DMS are monoclinic, space groupC2/c,Z=4,a=13.154(4),b=6.156(1),c=9.363(4)Å,=98.53(3)°. The structure was solved by direct methods and refined by leastsquares procedures to giveR=0.071 for 932 observed data. Crystals of DMO are monoclinic space group,P21/n,Z=2, witha=3.891(1),b=11.879(2),c=6.213(2) Å,=103.32(2)°. The structure is the same (within experimental error) as that reported by Dougill and Jeffrey (1953) and refined to giveR=0.074 for 395 observed data. 相似文献
2.
A core model approach to the calculation of deuteron quadrupole coupling constants is investigated using NH3 as an example. First the deuteron quadrupole coupling constant is calculated from a CNDO wave function. This result is subsequently improved by recomputing the N—D bond orbital by means of a variational calculation using the CNDO function to construct a core potential for the bond Hamiltonian. In order to simplify integrations a single-center basis is chosen to represent the variational wave function. A projection operator formalism is used as a computational scheme to maintain orthogonality of the bond orbital to core orbitals. Excellent agreement with experiment is obtained. The procedure is applicable to more complicated molecules. 相似文献
3.
A non-destructive method for the quantification of eleven elements in bone samples is described. The analytical scheme is based on short (30 s) irradiation with thermal neutrons followed immediately (decay time 10 s) by counting fluorine-20 for 30 s and, after a total waiting time of 150 s, by 10-min γ-spectrometry counting, which give data for Ca, Cl, Mg, Mn, Na, and V. Use of a boron carbide shield for a second set of irradiations with epithermal neutrons permits the additional determination of bromine and strontium and calculation of the contribution of aluminium and phosphorus to the total activity of 28Al. 相似文献
4.
The C-methylation of the potassium salt of 1-t-butyl-2-phenyl-3-(p-phenylbenzoyl)azetidine ( 1a ) with methyl iodide was studied in three solvents, and the stereochemical outcome of the reaction was shown to be dependent upon the solvent used. These results are rationalized in terms of the probable relative rates of the reaction in the various solvents and/or the effect of solvent on the structure of the anionic intermediate. Similar treatment of the potassium salt of 1-t-butyl-2-phenyl-3-benzoylazetidine ( 3a ) in ethyl ether gave a comparable result. The configurations of the epimeric C-methyl products ( 2a and 2b , and 4a ) were assigned on the basis of their spectral properties. With the aid of spectral data for a model compound, l-t-butyl-3-benzoyl-azetidine ( 5 ), several stereostructure-spectra relationships for 3-azetidinyl ketones are presented. 相似文献
5.
A series of different commercial membranes were characterized by their moisture absorption and desorption properties under controlled humidity and temperature conditions. This work was made possible by combining the features of a constant humidity conditioning chamber with those of a thermogravimetric (TG) apparatus. These two modules were interconnected by tubing, rotameters, an atmosphere-recycling microbellows pump and switching valves. Under programmed heating and isothermal conditions reproducible data were obtained in terms of weight-gain or weight-lossvs. time and pore size. Evaluation of the resulting TG curves allowed us to report reasonable differences in the materials, some of which had been previously surface-modified by the manufacturer. 相似文献
6.
We describe sufficient conditions for transferring from locally compact abelian groups to measure spaces the weak-type bounds
of maximal operators defined by multipliers of weak type. This leads to homomorphism theorems for maximal multiplier operators.
Communicated by Guido Weiss 相似文献
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A potentiometric method using a glass electrode has been applied to determination of ionization constants for deuterium oxide (D2O) in binary mixtures of D2O with dioxane, tetrahydrofuran, acetone, dimethylsulfoxide, CH3CH2OD, and CH3OD at 25°C. The results are compared with values of ionization constants for H2O obtained previously in the corresponding H2O-organic mixtures, and the isotope effect is shown to be small. Further calculations with the D2O results show that the first five solvents mentioned above are neither appreciably acidic nor basic in D2O solution, but that CH3OD shows slightly acidic behavior (pKa=16.0±0.3). 相似文献