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111.
Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained. 相似文献
112.
Karl Heinz Neeb Herbert Neidl und Heinz Stöckert 《Fresenius' Journal of Analytical Chemistry》1972,259(4):265-268
Zusammenfassung Zur Bestimmung der U- und Th-Gehalte in 0,5–1,5mg wiegenden Mikroproben von ThO2-UO2-Kernbrennstoffen wurde die Neutronenaktivierungsanalyse mit zerstörungsfreier-Spektrometrie eingesetzt. Bei Gehalten über 0,1% beträgt die relative Standardabweichung 6%. Der Th-Gehalt der Mikroproben wird durch-spektrometrische Messung des233Pa ermittelt; bei Natur-Uran enthaltenden Proben wird der U-Gehalt über239Np bestimmt, bei hochangereichertes UO2 enthaltenden Proben über131J. Mit der beschriebenen Methode können sowohl unbestrahlte als auch bestrahlte ThO2-UO2-Kernbrennstoffe untersucht werden.
Teil I siehe [3].
Herrn G. Hofmann danken wir für die Entnahme der Mikro-Bohrproben aus den bestrahlten und unbestrahlten Brennstoffschliffen. 相似文献
Use of a Ge(Li) detector in radiochemical analysisII. determination of U and Th contents in microsamples of ThO2-UO2 nuclear fuels
Neutron activation analysis with non-destructive-spectrometry has been used to determine U and Th in microsamples (0.5–1.5 mg) from ThO2-UO2 nuclear fuels. With U contents of more than 0.1% the relative standard deviation amounts to 6%. Th in the microsamples is estimated by measuring233Pa; in natural UO2 containing samples239Np ist measured for U determination, in highly enriched UO2 samples131J. Fresh und spent ThO2-UO2 nuclear fuels can be investigated by the method described.
Teil I siehe [3].
Herrn G. Hofmann danken wir für die Entnahme der Mikro-Bohrproben aus den bestrahlten und unbestrahlten Brennstoffschliffen. 相似文献
113.
Ralf Eiden Ralf Falter Barbara Augustin-Castro Heinz Friedrich Schöler 《Analytical and bioanalytical chemistry》1997,357(4):439-441
Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high
performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for
the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this
method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within
their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition
method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples
were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight.
Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996 相似文献
114.
115.
116.
Leibold C Foropoulos J Marsden HM Shreeve JM Oberhammer H 《Inorganic chemistry》2002,41(23):6125-6128
A gas-phase electron diffraction study of the azoxy compound which was synthesized by the reaction of CF3NO with N2F4 in a Pyrex glass vessel results in a trans CF3N(O)NF structure (F trans to CF3), although quantum chemical calculations (MP2 and B3LYP) predict a greater stability of the cis CF3NN(O)F isomer by about 12 kcal/mol. The CF3 group eclipses the N=N double bond. The following skeletal geometric parameters (r(a) values with 3sigma uncertainties) were obtained: N=N 1.287(15) A; N=O 1.231(6) A; N-F 1.380(6) A; N-C 1.498(6) A; N=N=O 131.2(13) degrees; N=N-F 103.5(13) degrees; N=N-C 114.0(12) degrees. The bond lengths in CF3N(O)NF are compared to those in azo, nitryl, and nitrosyl compounds with fluorine and/or CF3 substituents. 相似文献
117.
A New Aminoazirine Reaction. Formation of 3,6-Dihydropyrazin-2(1H)-ones The reaction of 3-(dimethylamino)-2H-azirines 1 and 2-(trifluoromethyl)-1,3-oxazol-5(2H)-ones 5 in MeCN or THF at 50–80° leads to 5-(dimethylamino)-3,6-dihydropyrazin-2(1H)-ones 6 (Scheme 3). Reaction mechanisms for the formation of 6 are discussed: either the oxazolones 5 react as CH-acidic heterocycles with 1 (Scheme 4), or the azirines 1 undergo a nucleophilic attack onto the carbonyl group of 5 (Scheme 6). The reaction via intermediate formation of N-(trifluoroacetyl)dipeptide amide 8 (Scheme 5) is excluded. 相似文献
118.
Ulrike Gabriella Wagner Christoph Kratky Heinz Falk Heinz Flödl 《Monatshefte für Chemie / Chemical Monthly》1987,118(10):1185-1194
The crystal structure of the pentapyrrin1 was determined by X-ray diffraction methodes at two temperatures (298K and 97K). It is the first structure determination of a linear polypyrrole with more than four pyrrole rings. In the crystal, the molecule is located on a crystallographic two-fold axis, which passes through the central pyrrole ring. It assumes a helical overall-conformation, which is stabilized by intramolecular hydrogen bonding. The acidic proton at the nitrogen atom of the central pyrrolic ring is disordered, being observed with half occupancy at two symmetry-equivalent positions off the crystallographic diad. Attempts to remove the disorder by cooling to 97K were unsuccessful, since no indication for a phase transition was detected. 相似文献
119.
Accurate nonadiabatic lower and upper bounds for groundstate energies of H
2
+
and D
2
+
are calculated with the linearized method of variance minimization. The results in a.u. are –0.597139063<E
0(H
2
+
)<–0.597138994 –0.598788775<E
0(D
2
+
)<–0.598778738 i.e. the values are determined with an absolute error smaller than 0.02 cm–1 for H
2
+
and 0.01 cm–1 for D
2
+
. 相似文献
120.