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排序方式: 共有1767条查询结果,搜索用时 15 毫秒
71.
Jose Castro‐Perez Nathan Hatcher Nana Kofi Karikari Sheng‐Ping Wang Vivienne Mendoza Henry Shion Alan Millar John Shockcor Mark Towers David McLaren Vinit Shah Stephen Previs Karen Akinsanya Michele Cleary Thomas P. Roddy Douglas G. Johns 《Rapid communications in mass spectrometry : RCM》2014,28(22):2471-2479
72.
73.
Justin J. Maresh Sonia E. Chavez Matthew J. Asciutto Nathan D. Brown Alexander A. Delgado Youya Gao 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):683-688
Electrophilic trisubstituted ethylenes, phenoxy ring-substituted methyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO2CH3, where R is 4-(4-BrC6H5O), 2-(4-ClC6H5O), 3-(4-ClC6H5O), 4-(3-ClC6H5O), 4-(4-ClC6H5O), 4-(4-FC6H5O), 2-(3-CH3OC6H5O), 2-(4-CH3OC6H5O), 3-(4-CH3OC6H5O), 4-(4-CH3OC6H5O), 3-(4-CH3C6H5O) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of phenoxy ring-substituted benzaldehydes and methyl cyanoacetate, and characterized by CHN analysis, IR, 1H and 13C-NMR. All the ethylenes were copolymerized with styrene (M1) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r1) for the monomers is 4-(4-CH3OC6H5O) (6.07) > 3-(4-ClC6H5O) (3.38) > 3-(4-CH3OC6H5O) (2.78) > 4-(3-ClC6H5O) (2.77) > 2-(4-ClC6H5O) (2.29) > 3-(4-CH3C6H5O) (1.98) > 4-(4-FC6H5O) (1.92) > 4-(4-ClC6H5O) (1.89) > 2-(3-CH3OC6H5O) (1.39) > 2-(4-CH3OC6H5O) (0.90) > 4-(4-BrC6H5O) (0.77). Relatively high Tg of the copolymers in comparison with that of polystyrene indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200-500°C range with residue (2.5-8.0% wt), which then decomposed in the 500-800°C range. 相似文献
74.
75.
Nathan J. Downs Peter W. Schouten Alfio V. Parisi 《Photochemistry and photobiology》2013,89(5):1234-1243
Fringing coral reefs provide a unique opportunity to study shallow aquatic ecosystems. A fringing coral reef system located in close proximity to a developed region was considered in this study. In such an environment, the rate of decay of dissolved organic matter is high and the penetration of higher energy ultraviolet‐B (UVB) extends a greater influence on species diversity, particularly upon shallow benthic communities. Results from a 9 month subsurface UVB exposure measurement campaign performed at a site located on the southern Queensland coast (Hervey Bay, 25°S) are presented in this research. For this, a novel dosimetric technique was utilized to measure long‐term subsurface UVB exposures. The resultant data set includes exposure measurements made during the significant La Niña event of late 2010 which resulted in unprecedented high sea surface temperatures and severe flooding across eastern Australia, impacting upon the lagoon regions of the Great Barrier Reef and Queensland's southern estuaries, including the study site. The influence of season, diurnal tidal variation, cloud cover and solar zenith angle were analyzed over the campaign period. Mean minimum daylight water depth was found to be the most significant factor influencing subsurface UVB. 相似文献
76.
Alicia M. Phelps Nicholas S. Dolan Nathan T. Connell Jennifer M. Schomaker 《Tetrahedron》2013,69(27-28):5614-5621
A versatile intramolecular reaction of allene-containing diazomalonates that exhibits excellent chemoselectivity for either allenic C–H insertion or cyclopropanation is demonstrated. The identity of the product depends on the transition metal catalyst that is employed for the reaction. Rh catalysts promote exclusive C–H insertion with good diastereoselectivity for the trans product, while Cu catalysis enables intramolecular cyclopropanation to yield methylenecyclopropanes with moderate to good E:Z ratios. 相似文献
77.
Rohan J. Williams Nathan W. McGill Jonathan M. White Spencer J. Williams 《Journal of carbohydrate chemistry》2013,32(5):236-263
Variable yields and glycosylation stereoselectivity were obtained for NIS/TfOH-medi- ated reaction of 4-methoxyphenyl 2,4,6-tetra-O-acetyl-β-D-galactopyranoside and thiogalactosides bearing acetyl, benzoyl, 2,6-dimethoxylbenzoyl, 2,4,6-trimethylbenzoyl, or 2,6-dichlorobenzoyl groups at the 2-positions and acetyl at the remainder. X-ray structures of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyr anoside and 4-methylphenyl 3,4-O-isopropylidene-2,6-di-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside revealed slightly distorted 4 C 1 chair conformations. Variable temperature NMR revealed that activation of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside afforded only dioxolenium ion, whereas 4-methylphenyl 3,4,6-tri-O-acetyl-2-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside gave a 1:1 mixture of dioxolenium ion and glycosyl triflate. However, the reaction intermediates formed from these deactivated donors do not influence the glycosylation stereoselectivity; instead, it is influenced by steric and electronic interactions at the transition states. 相似文献
78.
Jinxiong Lin Dr. Friedrich Wossidlo. Dr. Nathan T. Coles Manuela Weber Dr. Simon Steinhauer Priv.-Doz. Dr. Tobias Böttcher Prof. Dr. Christian Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202104135
A phosphinine-borane adduct of a Me3Si-functionalized phosphinine and the Lewis acid B(C6F5)3 has been synthesized and characterized crystallographically for the first time. The reaction strongly depends on the nature of the substituents in the α-position of the phosphorus heterocycle. In contrast, the reaction of B2H6 with various substituted phosphinines leads to an equilibrium between the starting materials and the phosphinine–borane adducts that is determined by the Lewis basicity of the phosphinine. The novel phosphinine borane adduct ( 6 -B(C6F5)3) shows rapid and facile insertion and [4+2] cycloaddition reactivity towards phenylacetylene. A hitherto unknown dihydro-1-phosphabarrelene is formed with styrene. The reaction with an ester provides a new, facile and selective route to 1-R-phosphininium salts. These salts then undergo a [4+2] cycloaddition in the presence of Me3Si−C≡CH and styrene to cleanly form unprecedented derivatives of 1-R-phosphabarrelenium salts. 相似文献
79.
Ashley J. Basson Dr. Nathan R. Halcovitch Dr. Mark G. McLaughlin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(48):e202201107
A range of highly functionalized polycyclic fragments have been synthesized, employing a catalytic dehydrative cyclization. A range of nucleophiles are shown to be successful, with the reaction producing numerous high value motifs. 相似文献
80.
Neel Sisodia Monica Miranda Kay L. McGuinness Jay D. Wadhawan Nathan S. Lawrence 《Electroanalysis》2021,33(3):559-562
This work presents the electrochemical response of a 2-(methylthio)phenol glassy carbon based electrode for a promising voltammetric pH sensor in both buffered and low-buffered solutions. Electropolymerization of the redox species was performed with the resulting polymer presenting a Nernstian response in buffered media, with a sensitivity of 51 mV/pH unit. The effectiveness of the sulfhydryl bond to facilitate proton transfer from the bulk solution to the phenol molecules has been confirmed, providing an accurate pH measurement of 8.28 in sea water media, compared to that measured with a calibrated glass pH probe of 8.30. 相似文献