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61.
Simon G. Bott Duddu Raja Gopal Annavajhula Durga Prasad Alan P. Marchand 《Journal of chemical crystallography》1993,23(12):1013-1017
The structure of a compound derived from a symmetrical cage diketone in which one of the ketone C=O groups has been converted into a ketal is reported. An investigation into reasons for the selective functionalization resulted in the isolation of acis, cisoid, cis linear triquinane derivative in which both ketones are converted to ketals that share a transannular oxygen atom. Crystal data:2, monoclinic,P21/c,a=7.6298(9),b=7.673(3),c=22.125(3)Å,=97.59(1)°,V=1283.9(5)Å3, andR=0.048 (1001 reflections);4, triclinic,P¯1,a=7.3864(9),b=9.6362(9),c=10.3889(9)Å,=75.749(6),=76.300(8), =83.100(8)°,V=694.8(4)Å3, andR=0.088 (1284 reflections). 相似文献
62.
Hydrazine sulphate is proposed as a primary standard reagent for the direct titrimetric determination of vanadium(V) and chromium(VI) alone and in mixtures with potentiometric and photometric end-points, in 9–12 M phosphoric acid medium. The methods proposed possess advantages over those currently available. The use of phosphoric acid as a reaction medium not only accelerates the hydrazine-vanadium(V) reaction very much but also makes it follow an accurate stoichiometric path. 相似文献
63.
A novel synthetic approach is described to incorporate one more carbon atom at C-2 position of phospholane oxides as homologated allylic alcohol by treatment of erythro-2,3-epoxy-3-methylphospholane 1-oxides with excess of dimethylsulfonium methylide. 相似文献
64.
[reaction: see text] The studies in the Diels-Alder reactions of 5-methoxy-masked o-benzoquinone (1a, R = OMe) and simple dissymmetric 2,4-cyclohexadienones 1b-e with methyl vinyl ketone, styrene, and benzyl vinyl ether are described. The dienones 1b-e reacted with dienophiles to form syn adducts (dienophile approach is syn to allylic methoxy group) exclusively. 相似文献
65.
1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields via a three-component coupling of secondary alcohols, alkynes and trimethylsilyl azide (TMSN3). This one-pot reaction occurs through in situ generation of an azide from the alcohol and TMSN3, followed by 1,3-dipolar cycloaddition of the terminal alkyne to afford the corresponding disubstituted triazoles. 相似文献
66.
Hari Gopal Mukerjee 《Fresenius' Journal of Analytical Chemistry》1958,163(2):87-90
Summary Change of concentration of electrolyte such as sodium chloride, potassium chloride, ammonium chloride and potassium bromide has a marked effect on the direction of migration of Cd. A very cheap set incorporating a number of Durrum'S units suitable for separation of a large number of different types of mixtures of ions has been devised. 相似文献
67.
New PNA analogues derived from aminoethylpyrrolidin-5-one backbone show stabilization of aepone-PNA:DNA hybrids and destabilization of the corresponding RNA hybrids compared to unmodified PNA. 相似文献
68.
Crystals of Co3(AsO4)2 were grown from the melt of a mixture of Co2As2O7 and As2O5. The crystals are isostructural with Mg3(AsO4)2 and are tetragonal with a = 6.858(2), c = 18.872(5) Å, Z = 6, and space group . A total of 1048 independent reflections were measured by diffractometer and used in the full-matrix refinement to a final R value of 0.069. The structure contains two distinct AsO4 groups. Two of the cobalt ions are octahedrally coordinated and a third occupies a site with four short and four long CoO distances. The crystal structure of Co3 (AsO4)2 is not based on the continuous three-dimensional closest packing of oxygen atoms. Nevertheless the number of oxygen atoms per cubic centimeter is 5.4 × 1022, which falls in the range of values for hexagonal and cubic closest packed structures. A better measure of the degree to which closest packing is achieved by a structure is suggested. It is based on an analysis of the polyhedra of oxygen atoms which surround each of the oxygen atoms in a structure and their relation to the polyhedra in ideally closest packed structures. In order to facilitate the analysis, polytopes of 11- and 12-vertex polyhedra were studied. A new decahexahedral 11-vertex polyhedron was found. 相似文献
69.
P. Ramachandra T. Siva Rama Krishna Gautam R. Desiraju 《Journal of Chemical Sciences》1989,101(4):327-334
The compound 3-hydroxy-6-(4′-nitro)phenylazopyridine (1) was observed to incorporate several organic solvents of crystallisation, forming stable clathrates. These clathrates decompose
upon heating and the host material is chemically transformed. Single crystal X-ray diffraction studies on the ethanol clathrate
lead to a reasonable model for the host structure. But the guest molecules are severely disordered. Alternatively, the compound
forms twinned crystals. The chemically closely related compound2 does not form clathrates. 相似文献
70.
[Reaction: see text]. The potential dual behavior as dienes and dienophiles of the diene moieties of masked o-benzoquinones (MOBs) 10a-e-12a-e, generated upon oxidation of 2-methoxyphenols 1-3 with BTIB in the presence of appropriate dienols, in their intramolecular Diels-Alder (IMDA) reactions has been examined. The IMDA reactions of MOBs 10a-d, 11a,b,d, and 12a,b,d resulted in highly functionalized oxatricyclic compounds 18a-d, 19a,b,d, and 20a,b,d, respectively, with concomitant formation of cis-decalin derivatives 21a-d, 22a,b,d, and 23a,b,d in a highly regio- and stereoselective manner. However, the MOBs 10e-12e provided exclusively oxatricyclic compounds 18e-20e. The formation of cis-decalins in these IMDA reactions illustrates the dienophilic character of MOBs, in addition to their behavior as dienes. The ratio of the two cycloadducts obtained in each reaction as a result of the dual character of MOBs depends on the nature and/or position of the substituents on both the cyclohexadienone moiety and the added 2,4-dienol. The majority of the cycloadducts resulted from the diene property of MOBs in intramolecular Diels-Alder reactions smoothly underwent Cope rearrangement to furnish cis-decalins as sole products in excellent to quantitative yields that provides a short and efficient entry to polyfunctionized cis-decalins from 2-methoxyphenols. Furthermore, the variation of dienophilic and diene characters of MOBs in the IMDA reactions with the electron-donating or electron-withdrawing substituent of both cyclohexadienone moiety and the added conjugated acyclic diene or 2,4-dienol has been studied in detail. 相似文献