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181.
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
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185.
RAMAN and IR spectroscopic investigation of alkyl derivatives of arsenic acid. II. Vibrational spectra of some alkanearsonic acid dialkylesters RAMAN and IR spectra of CH3AsO(OCH3)2, CH3AsO(OC2H5)2, C2H5AsO(OCH3)2, and C2H5AsO(OC2H5)2, are communicated and discussed. Their skeleton CAsO(OC)2 has very probably Cs symmetry. 相似文献
186.
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
187.
Leibold C Alvarez RM Cutin EH Della Vedova CO Oberhammer H 《Inorganic chemistry》2003,42(13):4071-4075
The IR (gas) and Raman (liquid) spectra of FC(O)NSCl(2) demonstrate the presence of a conformational mixture in both phases. According to a gas electron diffraction study, the main conformer (94(8)%) possesses a syn-syn structure (C(O)F group synperiplanar with respect to the SCl(2) bisector and the C=O bond synperiplanar to the N=S bond). Quantum chemical calculations (HF, B3LYP and MP2 with 6-31G basis set, and MP2/6-311(2df)) predict a syn-anti structure for the second conformer. Analysis of the IR (gas) spectrum results in a contribution of 5(1)% of the minor form, corresponding to a Gibbs free energy difference DeltaG degrees = G degrees (syn-anti) - G degrees (syn-syn) = 1.75(15) kcal/mol. This value is reproduced very well by quantum chemical calculations, which include electron correlation effects (DeltaG degrees = 1.28-1.56 kcal/mol). The HF approximation overestimates this energy difference (DeltaG degrees = 3.24 kcal/mol). 相似文献
188.
H. Schumann F. H. Grlitz F. E. Hahn J. Pickardt Changtao Qian Zuowei Xie 《无机化学与普通化学杂志》1992,609(3):131-138
The partial hydrolysis of [O(CH2CH2C5H4)2]Y(C5H4CH3) 1 , [O(CH2CH2C5H4)2]Y(C5H5) 3 , and [O(CH2CH2C5H4)2]Ho(C5H4CH3) 5 results in the formation of [O(CH2CH2CH2C5H4)2Y(μ-OH)2]2 2 , (C5H5)3Y(OH2) 9 and (MeC5H4)3Ho(OH2) 11 . The new compounds have been characterized by elemental analyses, IR and NMR spectra. The X-ray structural analyses shows 2 to be monoclinic, space group P21/n with a = 1146.0(3), b= 1046.6(3), c = 1514.9(3) pm, β = 94.83(2)°. The molecular structure shows bridging hydroxyl groups with a mean distance Y? O = 223.8(3) pm. 11 crystallizes in the cubic space group 14 3d with a = 1847.9(3)pm with Z = 16 molecules per unit cell. The molecules posses symmetry C3-3, the coordination is trigonal pyramidal with three methylcyclopentadienyl anions and one water molecule as ligands. The distance Ho? O is 231 pm. 相似文献
189.
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
190.
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