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排序方式: 共有416条查询结果,搜索用时 156 毫秒
1.
Ozonolysis of a Series of Methylated Alkenes: Reaction Rate Coefficients and Gas‐Phase Products 下载免费PDF全文
Tristan Braure Véronique Riffault Alexandre Tomas Romeo Iulian Olariu Cecilia Arsene Yuri Bedjanian Patrice Coddeville 《国际化学动力学杂志》2015,47(9):596-605
The gas‐phase ozonolysis of three methylated alkenes, i.e., trans‐2,2‐dimethyl‐3‐hexene (22dM3H), trans‐2,5‐dimethyl‐3‐hexene (25dM3H), and 4‐methyl‐1‐pentene (4M1P), has been investigated in the presence of sufficient hydroxyl radical scavenger in a laminar flow reactor at ambient temperature (296 ± 2 K) and P = 1 atm of dry air (RH ≤ 5%). Ozone levels in the reactor were monitored by an automatic analyzer. Alkene and gas‐phase product concentrations were determined via online sampling either on three‐bed adsorbent cartridges followed by thermodesorption and GC/FID‐MS analysis or on 2,4‐dinitrophenylhydrazine (DNPH) cartridges for subsequent HPLC/UV analysis. Reaction rate coefficients of (3.38 ± 0.12) × 10?17 for 22dM3H and (2.71 ± 0.26) × 10?17 for 25dM3H, both in cm3 molecule?1 s?1 units, have been obtained under pseudo–first‐order conditions. Primary carbonyl products have been identified for the three investigated alkenes, and branching ratios are reported. In the case of 4M1P ozonolysis, the yield of a Criegee intermediate was indirectly determined. Kinetics and product study results are compared to those of literature when available. This work represents the first investigation of reaction products in the ozonolysis of 22dM3H, 25dM3H, and 4M1P in a flow reactor. 相似文献
2.
O. Volkova K. Klimov O. Savelieva N. Tristan E. Goodilin B. Buechner A. Vasiliev 《Journal of magnetism and magnetic materials》2006
Magnetic and transport properties of double distorted perovskites CaCuMn6O12 and CaCu2Mn5O12 are studied in a range 2–300 K. The leading role in magnetism of these compounds belongs to antiferromagnetic exchange interaction of Cu2+ in square coordination with Mn3+/Mn4+ in octahedral coordination. The values of saturation magnetization indicate that Mn3+ ions in square coordination are coupled ferromagnetically with Mn3+/Mn4+ in octahedral coordination. The colossal magnetoresistance in the pellet samples is due assumingly to intergranular spin-polarized tunneling of current carriers. 相似文献
3.
For several physically interesting Calabi-Yau manifolds, we count and parametrize gauge-neutral matter particles occurring in corresponding superstring compactifications. To this end, we use the technique of exact and spectral sequences and then describe and discuss our results in the more familiar tensor notation.Supported by the Robert A. Welch Foundation and the NSF Grant: PHY 8605978. On leave of absence from the Ruder Bokovi Institute, Bijenika 54, YU-41000 Zagreb, Croatia, Yugoslavia 相似文献
4.
5.
Fabrice Freville Tristan Richard Katell Bathany Serge Moreau 《Helvetica chimica acta》2006,89(12):2958-2974
A new strategy to cyclize short synthetic oligonucleotides on DNA or RNA target strands is described. The approach is based on metal‐templated cyclization of short synthetic oligonucleotides conjugated with two chelating 2,2′ : 6′,2′′‐terpyridine (Tpy) moieties at their 3′‐ and 5′‐ends. Cyclization after metal addition (Zn2+, Fe2+) was demonstrated by means of thermal‐denaturation experiments, MALDI‐Q‐TOF‐MS, and gel electrophoresis (PAGE). 1D‐ and 2D‐NMR Experiments were performed to analyze the association of complementary strands after metal‐mediated cyclization. Our protocol allows the efficient circularization of synthetic oligonucleotides. Thereby, the hybridization on a complementary strand was more efficient with an RNA target strand and a 2′‐O‐methylated circularized oligomer. 相似文献
6.
Drew MG Hill C Hudson MJ Iveson PB Madic C Youngs TG 《Dalton transactions (Cambridge, England : 2003)》2004,(2):244-251
The extracting agent 2,6-bis(4,6-di-pivaloylamino-1,3,5-triazin-2-yl)-pyridine (L(5)) in n-octanol was found, in synergy with 2-bromodecanoic acid, to give D(Am)/D(Eu) separation factors (SFs) between 2.4 and 3.7 when used to extract the metal ions from 0.02-0.12 M HNO(3). Slightly higher SFs (4-6) were obtained in the absence of the synergist when the ligand was used to extract Am(III) and Eu(III) from 0.98 M HNO(3). In order to investigate the possible nature of the extracted species crystal structures of L(5) and the complex formed between Yb(III) with 2,6-bis(4,6-di-amino-1,3,5-triazin-2-yl)-pyridine (L(4)) were also determined. The structure of L(5) shows 3 methanol solvent molecules all of which form 2 or 3 hydrogen bonds with triazine nitrogen atoms, amide nitrogen or oxygen atoms, or pyridine nitrogen atoms. However, L(5) is relatively unstable in metal complexation reactions and loses amide groups to form the parent tetramine L(4). The crystal structure of Yb(L(4))(NO(3))(3) shows ytterbium in a 9-coordinate environment being bonded to three donor atoms of the ligand and three bidentate nitrate ions. The solvent extraction properties of L(4) and L(5) are far inferior to those found for the 2,6-bis-(1,2,4-triazin-3-yl)-pyridines (L(1)) which have SF values of ca. 140 and theoretical calculations have been made to compare the electronic properties of the ligands. The electronic charge distribution in L(4) and L(5) is similar to that found in other terdentate ligands such as terpyridine which have equally poor extraction properties and suggests that the unique properties of L(1) evolve from the presence of two adjacent nitrogen atoms in the triazine rings. 相似文献
7.
A titrimetric study of the reaction between chloramine-T (CAT) and ammonia is described. The effects of the presence of bromide, the ratio of CAT to ammonia concentrations, the time for reaction and the pH of the reaction media are all significant in the quantitativeness of the reaction that occurs. 相似文献
8.
Janis Jermaks Phong K. Quach Zara M. Seibel Julien Pomarole Tristan H. Lambert 《Chemical science》2020,11(30):7884
A computational and experimental study of the hydrazine-catalyzed ring-opening carbonyl–olefin metathesis of norbornenes is described. Detailed theoretical investigation of the energetic landscape for the full reaction pathway with six different hydrazines revealed several crucial aspects for the design of next-generation hydrazine catalysts. This study indicated that a [2.2.2]-bicyclic hydrazine should offer substantially increased reactivity versus the previously reported [2.2.1]-hydrazine due to a lowered activation barrier for the rate-determining cycloreversion step, a prediction which was verified experimentally. Optimized conditions for both cycloaddition and cycloreversion steps were identified, and a brief substrate scope study for each was conducted. A complication for catalysis was found to be the slow hydrolysis of the ring-opened hydrazonium intermediates, which were shown to suffer from a competitive and irreversible cycloaddition with a second equivalent of norbornene. This problem was overcome by the strategic incorporation of a bridgehead methyl group on the norbornene ring, leading to the first demonstrated catalytic carbonyl–olefin metathesis of norbornene rings.A computational and experimental study has uncovered a second generation hydrazine that enables the catalytic ring-opening carbonyl–olefin metathesis of norbornenes. 相似文献
9.
THz spectroscopic investigation of 2,4-dinitrotoluene 总被引:5,自引:0,他引:5
Yunqing Chen Haibo Liu Yanqing Deng Dunja Schauki Michael J. Fitch Robert Osiander Caroline Dodson James B. Spicer Michael Shur X.-C. Zhang 《Chemical physics letters》2004,400(4-6):357-361
We have investigated the terahertz (THz) spectrum of 2,4-DNT by using Fourier transform infrared spectroscopy in the 0.2–19.5 THz region. We also examined low-frequency intermolecular or phonon modes between 0.2 and 1.8 THz via THz time-domain spectroscopy. The extracted absorption coefficient and refractive index of an intermolecular band at 1.08 THz are 110 cm−1 and 1.67, respectively. Density functional theory (DFT) was applied to obtain structure and vibrational frequencies of 2,4-DNT. The calculated results are in agreement with the experimental data. Observed vibrational frequencies have been interpreted using DFT. Two intermolecular or phonon modes were identified at 1.08 and 2.52 THz. 相似文献
10.
The photometric determination of aluminium by automated colour development with Xylenol Orange is described. The reagent has been found to act faster if used in alcohol solution. 相似文献