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91.
92.
Nguyen Ba Chanh Christian Hauw Alain Meresse Madeleine Rey-Lafon Laure Ricard 《Journal of Physics and Chemistry of Solids》1985,46(12):1413-1420
The existence of three main crystalline phases (called III, II and I) in (C12H25NH3)2CdCl4 has been revealed by differential scanning calorimetry. X-ray diffraction and spectroscopic studies. The crystal- lographic evolution with increasing temperature appears to be monoclinic (III) → orthorhombic (II) → tetragonal (I). The low temperature phase III is the only ordered structure. The phase transition (III-II), which is of first order type, corresponds to an order-disorder mechanism involving the organic part of the structure (alkylammonium chains) whereas the phase transition (II-I), which is of second-order type, is related to the arrangement of the mineral matrix (octahedra of perovskite layers). An intermediate disordered form II', stable in a very narrow temperature range and structurally similar to the form II, has also been observed, so that the transformation (III-II) proceeds, in fact, in two steps (III-II'-II). The variation enthalpies observed at the transitions (III-II'-II) and analyzed through an order-disorder mechanism demonstrate the high disorder of the alkylammonium chains in form II, in agreement with spectroscopic results. No thermal anomaly or spectroscopic modification is observed for the high temperature transition (II-I). 相似文献
93.
Atom transfer cyclization reactions (ATRC) provide rapid access to functionalized γ-butyrolactones. 相似文献
94.
95.
Treatment of the thf adduct UO2(NCN)thf (NCN = [(Me3SiN)CPh(NSiMe3)]) (1) with 2 equiv of B(C6F5)3 provides UO{OB(C6F5)3}(NCN)2 (2) the first example of a neutral uranyl complex exhibiting Lewis basic behavior. The crystal structure of 2 shows a U=O-B interaction with an elongated U=O bond (1.898(3) A). Raman spectroscopy suggests weakening of the O=U=O bonding, giving the lowest reported symmetric stretching frequency for a monomeric uranyl complex, nu1 = 780 cm-1. The borane can be selectively removed using PMe3 to give the coordinatively unsaturated UO2(NCN)2 (3) or using tBuNC to provide UO2(CNBut)(NCN)2 (4), the first example of an isonitrile coordinated to uranium. 相似文献
96.
Michael R.L. Stratford Madeleine F. Dennis Ralph Cochrane Charles S. Parkins Steven A. Everett 《Journal of chromatography. A》1997,770(1-2):151-155
The short lifetime of nitric oxide (NO) in vivo impedes its quantitation directly; however, the determination of nitrite and nitrate ions as the end-products of NO oxidation has proven a more practical approach. High-performance ion chromatographic analysis of nitrite in biological fluids is hampered by the large amount of chloride ion (up to 100mmol/l) which results in insufficient peak resolution when utilizing conductimetric detection. Analysis of both anions in small sample volumes is also constrained by the need to minimise sample handling to avoid contamination by environmental nitrate. We report a means to remove Cl− ions from small sample volumes using Ag+ resin which facilitates quantitation of either nitrite and nitrate anions in biological samples, using silica or polymer based ion-exchange resins with conductimetric or electrochemical and spectrophotometric detection. Including a reversed-phase guard column before the anion-exchange guard and analytical column also greatly extends column lifetime. 相似文献
97.
Haeffner F Jacobson MA Keresztes I Williard PG 《Journal of the American Chemical Society》2004,126(51):17032-17039
A density functional theory (B3LYP/6-31+G) study was undertaken in an effort to learn more about the mechanisms controlling the regioselective deprotonations of the synthetically versatile N-lithio-N-(tert-butyl)allylamide 1 and N-lithio-N-(trimethylsilyl)allylamine 2 compounds. The calculations suggest that deprotonation of 1 occurs exclusively at the allylic position. This agrees with experimental results. The calculations also suggest that deprotonation of allylamine 2 exclusively at the cis-vinylic position is due to kinetic control. 相似文献
98.
Donohoe TJ Raoof A Freestone GC Linney ID Cowley A Helliwell M 《Organic letters》2002,4(18):3059-3062
[reaction: see text] The stereoselective Birch reduction of 3-methyl-2-furoic acids using a readily available chiral auxilairy is described; by coupling this process to an oxidative cleavage/aldol ring closure sequence we were able to produce highly functionalized and enantiopure dihydropyranones in high yield. This sequence has ample flexibility built into it, either by the use of different electrophiles during reductive alkylation or by subsequent derivatization of the dihydropyranone after ring expansion. 相似文献
99.
A number of 1,4-addition reactions of 4,7-benzimidazoledione with hydrogen halides, thiols and amines are described. 相似文献
100.
A three-step synthesis of 11-dodecynal is described. 相似文献