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101.
Chatgilialoglu C Ferreri C Guerra M Timokhin V Froudakis G Gimisis T 《Journal of the American Chemical Society》2002,124(36):10765-10772
Relative kinetic data were determined for the 5-endo-trig cyclization of radical 12 compared to hydrogen abstraction from (TMS)(3)SiH in the temperature range of 344-430 K, which allows for the estimation of a rate constant of 2 x 10(4) s(-)(1) at 298 K with an activation energy of ca. 9 kcal/mol for the cyclization process. The 5-endo-trig cyclization of a variety of radicals that afford five-membered nitrogen-containing heterocycles was addressed computationally at the UB3LYP/6-31G level. The 5-endo vs 4-exo mode of cyclication and the effect of delocalization of the unpaired electron in the transition state were investigated. Because the ring formed during cyclization contains five sp(2) centers, electrocyclization via a pentadienyl-like resonance form was also considered. For comparison, similar calculations were performed for 4-penten-1-yl and related radicals. The factors that affect the activation energies of homolytic 5-endo-trig cyclization were determined. In the absence of steric or conformational effects, the endo cyclization to form the five-membered ring was strongly favored over exo cyclization to form the four-membered ring not only on thermodynamic grounds but also kinetically. When a substituent on the double bond was able to delocalize the unpaired electron in the transition state of the 4-exo path, the two modes of cyclization became kinetically comparable. These results have an important bearing on the generalization of the Baldwin-Beckwith rules, which classified the 5-endo-trig radical cyclization as a "disfavored" process. 相似文献
102.
Brice JL Harang JE Timokhin VI Anastasi NR Stahl SS 《Journal of the American Chemical Society》2005,127(9):2868-2869
The first examples of palladium-catalyzed oxidative amination of unactivated alkyl olefins have been identified. To be successful, these reactions must be conducted under cocatalyst-free conditions that involve direct dioxygen-coupled turnover of the palladium catalyst. The oxidative amination products of norbornene and other cyclic alkenes implicate a cis-aminopalladation mechanism. 相似文献
103.
Polarity control and residual strain in ZnO epilayers grown by molecular beam epitaxy on (0001) GaN/sapphire 下载免费PDF全文
Md. Barkat Ullah Vitaliy Avrutin Si Qian Li Saikat Das Morteza Monavarian Mykyta Toporkov Ümit Özgür Pierre Ruterana Hadis Morkoç 《固体物理学:研究快报》2016,10(9):682-686
We report on the polarity control of ZnO grown by plasma assisted molecular beam epitaxy on Ga polar (0001) GaN/sapphire templates simply via the oxygen‐to‐Zn (VI/II) ratio during the growth of a thin nucleation layer at 300 °C. Following Zn pre‐exposure, the ZnO layers nucleated with low VI/II ratios (<1.5) exhibited Zn‐polarity. Those nucleated with VI/II ratios above 1.5, exhibited O‐polarity. Supported by scanning transmission electron microscopic imaging, we have unequivocally demonstrated that polarity inversion takes place without formation of any vertical inversion domains and within one monolayer of presumably non‐stoichiometric GaOx formed at the ZnO/GaN interface. A direct correlation between polarity and strain sign of ZnO layers has been found. The Zn‐polar ZnO layers were under tensile biaxial strain, whereas the O‐polar material exhibited compressive strain. Moreover, the amount of residual strain varied linearly with VI/II ratio used during the low‐temperature nucleation layer growth. Strain control with VI/II ratio has been explained by the potential formation of Zn interstitials. 相似文献
104.
Importance of Micropore–Mesopore Interfaces in Carbon Dioxide Capture by Carbon‐Based Materials 下载免费PDF全文
Dr. Gema Durá Dr. Vitaliy L. Budarin Dr. José A. Castro‐Osma Dr. Peter S. Shuttleworth Sophie C. Z. Quek Prof. James H. Clark Prof. Michael North 《Angewandte Chemie (International ed. in English)》2016,55(32):9173-9177
Mesoporous carbonaceous materials (Starbons®) derived from low‐value/waste bio‐resources separate CO2 from CO2/N2 mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8–32 % versus 73 %) yet adsorb up to 65 % more CO2. The presence of interconnected micropores and mesopores is responsible for the enhanced CO2 adsorption. The Starbons® also showed three–four times higher selectivity for CO2 adsorption rather than N2 adsorption compared to AC. 相似文献
105.
Chebanov VA Saraev VE Desenko SM Chernenko VN Knyazeva IV Groth U Glasnov TN Kappe CO 《The Journal of organic chemistry》2008,73(13):5110-5118
Regio- and chemoselective multicomponent protocols for the synthesis of 1,4,6,7,8,9-hexahydro-1H-pyrazolo[3,4-b]quinolin-5-ones, 5,6,7,9-tetrahydropyrazolo[5,1-b]quinazolin-8-ones, and 5a-hydroxy-4,5,5a,6,7,8-hexahydropyrazolo[4,3-c]quinolizin-9-ones starting from 5-amino-3-phenylpyrazole, cyclic 1,3-dicarbonyl compounds and aromatic aldehydes are described. Whereas the three-component coupling in ethanol under reflux conditions provides mixtures of pyrazoloquinolinones and pyrazoloquinazolinones, the condensation can be successfully tuned toward the formation pyrazoloquinolinones (Hantzsch-type dihydropyridines) by performing the reaction at 150 degrees C in the presence of triethylamine base applying sealed vessel microwave or conventional heating. On the other hand, using sonication at room temperature under neutral conditions favors the formation of the isomeric pyrazoloquinazolinones (Biginelli-type dihydropyrimidines). These products are also obtained when the three-component condensation is executed in the presence of trimethylsilylchloride as reaction mediator at high temperatures. A third reaction pathway leading to pyrazoloquinolizinones in a ring-opening/recyclization sequence can be accessed by switching from triethylamine to a more nucleophilic base such as sodium ethoxide or potassium tert-butoxide. The reaction mechanism and intermediates leading to these three distinct tricyclic condensation products are discussed. 相似文献
106.
The Ginzburg number Gi of deuterated poly(butadiene) (dPB) and poly(styrene) (PS) homopolymer blend of critical composition mixed with a dPB-PS symmetric diblock copolymer was determined from small angle neutron scattering. A 3 orders of magnitude change of Gi was determined between binary polymer blend and diblock copolymer melt. The strongest change of Gi is observed within the isotropic Lifshitz regime of critical universality occurring over a 3% range of diblock concentration and interpolates the corresponding Gi of the 3D-Ising and Brasovskii regimes. A Lifshitz critical point was not observed consistent with the proposed lower critical dimension d(LCP)=4. 相似文献
107.
Ekaterina A. Filatova Anna V. Gulevskaya Alexander F. Pozharskii Vitaliy V. Suslonov 《Tetrahedron》2018,74(1):165-173
The Sonogashira coupling of 2-ethynyl, 4-ethynyl and 2,7-diethynyl derivatives of 1,8-bis(dimethylamino)naphthalene (proton sponge) with 1-iodo- and 1,8-diiodonaphthalenes has been studied. The reaction of the above alkynes with 1-iodonaphthalene gave the expected naphthylethynyl derivatives of proton sponge. At the same time, the coupling of 2-ethynyl- and 2,7-diethynyl-1,8-bis(dimethylamino)naphthalenes with 1,8-diiodonaphthalene resulted in the formation of N,N,7-trimethyl-7H-acenaphtho[1,2-b]benzo[g]indol-8-amines. The reaction of 1,8-diiodonaphthalene with 4-ethynyl-1,8-bis(dimethylamino)naphthalene produced 14-(4,5-bis(dimethylamino)naphthalen-1-yl)-N11,N11,N12,N12-tetramethylnaphtho[1,2-k]fluoranthene-11,12-diamine together with 4-((8-iodonaphthalen-1-yl)ethynyl)-N1,N1,N8,N8-tetramethylnaphthalene-1,8-diamine. It was suggested that the mechanisms of the two novel cascade transformations stem from the specific nature of the proton sponge substrates. 相似文献
108.
Interpolymer complexes of poly(acrylic acid) with poly(2-hydroxyethyl acrylate) in aqueous solutions
Grigoriy?A.?MunEmail author Vitaliy?V.?Khutoryanskiy Gulnara?T.?Akhmetkalieva Sergey?N.?Shmakov Artem?V.?Dubolazov Zauresh?S.?Nurkeeva Kinam?Park 《Colloid and polymer science》2004,283(2):174-181
Complexes formed from poly(acrylic acid) and poly(2-hydroxyethyl acrylate) were studied in aqueous solutions by viscometric, turbidimetric, FTIR spectroscopic, and thermogravimetric analysis methods. The formation of interpolymer complexes stabilized by hydrogen bonds was observed. It was found that the compositions of these interpolymer complexes are strongly dependent on the concentration of polymers, the order of mixing the solutions, and the pH. It was demonstrated that the complexation ability of poly(2-hydroxyethyl acrylate) is relatively low compared to other known nonionic water-soluble polymers. However, it can be significantly increased via hydrophobic modification of the poly(acrylic acid) using cetyl pyridinium bromide. 相似文献
109.
Alexander M. Puziy Olga I. Poddubnaya Anna Derylo-Marczewska Adam W. Marczewski Magdalena Blachnio Mykola M. Tsyba Vitaliy I. Sapsay Dmytro O. Klymchuk 《Adsorption》2016,22(4-6):541-552
Kinetics of bovine serum albumin and ovalbumin adsorption by nanoporous carbons with different main pore sizes (1.6, 5, 7.8 and 28 nm) was studied. Experimental kinetics curves were well described by multi-exponential equation with different number of exponents (from 1 to 4). Protein adsorption kinetics showed significant dependence on pore size of carbonaceous adsorbent. Correlation between pore size distribution and amount of protein adsorbed revealed threshold pore size 7.3 nm for BSA and 6.8 nm for OVA, which are close to hydrodynamic diameter of protein molecules. The fastest and the highest adsorption of proteins were observed in carbons having developed porosity with pore sizes larger than 15 nm. 相似文献
110.
Geometric and electronic structures of silicon fluorides
(N = 4 – 6) and potential energy surfaces for dissociation reactions
→ SiF4 + F– and
→
+ F– 下载免费PDF全文
Vitaliy V. Koval Ruslan M. Minyaev Vladimir I. Minkin 《International journal of quantum chemistry》2016,116(18):1358-1361
The geometric and electronic structures of a series of silicon fluorides (n = 4 ? 6) were computationally studied with the aid of density functional theory (DFT) method with B3LYP and M06‐2X functionals and coupled cluster (CCSD and CCSD(T)) methods with 6‐311++G(d,p) basis set. The nature of the Si‐F bonds in these compounds was analyzed in the framework of the natural bond orbital theory and natural resonance theory. Energy characteristics (heats of reactions and energy barriers) of the dissociation reactions → SiF4 + F– and → + F– were calculated using the DFT and CCSD methods. The potential energy surface of elimination of a fluoride anion from has a specific topology with valley‐ridge inflection points corresponding to bifurcations of the minimal energy reaction path. © 2016 Wiley Periodicals, Inc. 相似文献