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11.
Ong RA Weir AJ Abrams GS Amidei D Baden AR Barklow T Boyarski AM Boyer J Burchat PR Burke DL Butler F Dorfan JM Feldman GJ Gidal G Gladney L Gold MS Goldhaber G Golding L Haggerty J Hanson G Hayes K Herrup D Hollebeek RJ Innes WR Jaros JA Juricic I Kadyk JA Karlen D Klein SR Lankford AJ Larsen RR LeClaire BW Levi M Lockyer NS Lüth V Nelson ME Perl ML Petersen A Richter B Riles K Rowson PC Schaad T Schellman H Schmidke WB Sheldon PD Trilling GH Wood DR Yelton JM 《Physical review letters》1988,60(25):2587-2590
12.
13.
The structure of the complex, [Fe2(II)Fe2(III)(HCOO)10(C6H7N6)n, (1) exhibits a neutral two-dimensional layer network of alternating iron(II) and iron(III) ions, bridged equatorially by formate groups. All iron atoms are octahedrally coordinated, with iron(III) coordinating axially to one gamma-picoline and one formate group, while the iron(II) centers interact axially with two gamma-picoline groups, above and below the layer plane. The complex crystallizes in the triclinic space group P1 at all studied temperatures [at 120 K, the cell dimensions are: a = 10.228(1), b = 12.071(1), c = 12.072(1) A, alpha = 89.801(2), beta = 71.149(2), gamma = 73.371(2) degrees]. An intralayer antiferromagnetic exchange interaction of J = -2.8 cm(-1) between iron(II) and iron(III) was observed in the magnetic studies. Decreasing the temperature to close to 20 K causes a magnetic-ordering phenomenon to occur and a low-temperature phase with a long-range antiferromagnetic spin orientation appears. The magnetic phase transition was confirmed by M?ssbauer spectroscopic studies at temperatures above and below the critical temperature. Structural information of 1 from synchrotron X-ray diffraction data collected at room temperature and 16 K suggests that the antiferromagnetic ordering is caused by an enhanced pi-pi interaction between chi-picoline groups from adjacent layers. 相似文献
14.
Changes in the mass spectra with inlet temperature were used in this work to demonstrate the dependence of keto-enol tautomerism of acetylacetone, 3-methyl acetylacetone and 3-allyl acetylacetone on temperature. The largest dependence of temperature were shown by the ion [M ? 42]+. arising from a McLafferty type rearrangement and by the ion [M ? Me]+ resulting from simple α-cleavage. The ion [M ? 42]+. peak increases with the temperature of the inlet system while the ion [M ? Me]+ peak decreases. By assuming that the ion [M ? 42]+. represents the keto form and that the ion [M ? Me]+ represents the cis-enol form (stabilized by the hydrogen bond) one sees that the direction of the intensity variation of these peaks with temperature is in accord with the expected change of keto-enol tautomerism with temperature. A quantitative correlation on the basis of the above assumptions is also approached. Recording of the mass spectra of these three β-diketones at different energies of the incident electrons enables us to estimate whether or not the particular ions present in the mass spectra result from energetically favourable processes. The variation of the intensities of the peaks with the temperature of the inlet at different electron energies is also discussed. 相似文献
15.
Ian K. Boddy J. Boniface Richard C. Cambie Peter A. Craw David S. Larsen Hamish McDonald Peter S. Rutledge Paul D. Woodgate 《Tetrahedron letters》1982,23(42):4407-4408
Gentle heating of allyloxyanthraquinones with sodium dithionite in dimethylformanide - water effects a rapid and controlled rearrangement to give high yields of 2-allyanthraquinones. 相似文献
16.
Klein SR Himel TM Abrams G Amidei D Baden AR Barklow T Boyarski AM Boyer J Burchat PR Burke DL Butler F Dorfan JM Feldman GJ Gidal G Gladney L Gold MS Goldhaber G Golding L Haggerty J Hanson G Hayes K Herrup D Hollebeek RJ Innes WR Jaros JA Juricic I Kadyk JA Karlen D Lankford AJ Larsen RR LeClaire BW Levi M Lockyer NS Lüth V Matteuzzi C Nelson ME Ong RA Perl ML Petersen A Richter B Riles K Rowson PC Schaad T Schellman H Schmidke WB Sheldon PD Trilling GH de la Vaissiere C Wood DR Yelton JM 《Physical review letters》1987,58(7):644-647
17.
Gidal G Boyer J Butler F Cords D Abrams GS Amidei D Baden AR Barklow T Boyarski AM Burchat P Burke DL Dorfan JM Feldman GJ Gladney L Gold MS Goldhaber G Golding LJ Haggerty J Hanson G Hayes K Herrup D Hollebeek RJ Innes WR Jaros JA Juricic I Kadyk JA Karlen D Klein SR Lankford AJ Larsen RR LeClaire BW Levi ME Lockyer NS Lüth V Matteuzzi C Nelson ME Ong RA Perl ML Richter B Riles K Rowson PC Schaad T Schellman H Schmidke WB Sheldon PD Trilling GH de la Vaissière C Wood DR Yelton JM Zaiser C 《Physical review letters》1987,59(18):2016-2019
18.
Li W Nelson DP Jensen MS Hoerrner RS Javadi GJ Cai D Larsen RD 《Organic letters》2003,5(25):4835-4837
Imidazo[1,2-a]pyrimidine can be arylated at the 3-position with aryl bromides in the presence of base and a catalytic amount of palladium. This provides an efficient one-step synthesis of 3-arylimidazo[1,2-a]pyrimidines from the unsubstituted heterocycle. [reaction: see text] 相似文献
19.
A method for the determination of ethotoin and its p-hydroxylated and dealkylated metabolites in urine has been developed. Ethotoin and the metabolites were extracted from acidified urine with ethyl acetate and silylated before injection into a combined gas chromatograph--mass spectrometer. Four partly identified metabolites were recorded, but their exact quantitation was not possible as pure reference substances were not available. The limit of sensitivity was far below the amounts of ethotoin and of its metabolites found in urine from patients treated with therapeutic doses of ethotoin. 相似文献
20.
Larsen BR Astorga-Llorens C Florêncio MH Bettencourt AM 《Journal of chromatography. A》2001,926(1):167-174
With its detection limit well below 30 pg microl(-1) LC-MS-MS has become a sensitive and thus popular analytical technique for organoarsenical compounds. Collision induced dissociation (CID) is a valuable tool for speciation and facilitates a positive identification of the species detected. However, it is not straightforward to understand the fragmentation pathways of organoarsenical compounds when only CID-MS-MS data is available. In the present paper we have investigated multiple mass spectrometry (MSn, n=1, 2, 3, 4, 5, 6) with electrospray CID fragmentation for a number of organoarsenical compounds likely to occur in the environment. The investigated compounds were tetramethylarsonium, trimethylarsinoxide, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, and dimethylarsinoylethanol. By CID of (protonated) organoarsenical cations mostly even-electron fragments are produced after neutral loss processes such as elimination of H2, H2O, CH4, C2H2, C2H4, C2H6, HCHO, CH3OH, C2H5OH, C2H4O, and CH2CO. However, abundant odd-electron fragments are also formed after elimination of radical species. Evidence for reduction of As(V) to As(III) as a driving force in the odd-electron ion formation is obtained. 相似文献