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91.
Keto aldehydes were selectively converted to non-conjugated alkynyl ketones possessing an unsubstituted alkyne terminus using one-pot nonaflation—base catalyzed elimination reaction sequences. Consecutive one-pot nonaflation of keto aldehydes with perfluorobutane-1-sulfonyl fluoride and elimination of the nonaflyl group using the P1 phosphazene base resulted in the formation of a terminal CC triple bond with the keto group remaining intact. Careful optimization of the reaction conditions enabled a highly chemoselective conversion of the aldehyde function in the presence of unprotected keto groups exploiting a minor difference in acidity of their α-hydrogen atoms. Scope and limitations of the protocol as well as possible implementation of these substrates in Sonogashira coupling were explored. 相似文献
92.
A discussion of proficiency testing (PT) topics started by Heydorn (Accred Qual Assur 15:643–645, 2010) is continued in the present paper. The role of PT in the accreditation of testing/analytical laboratories, the use of consensus
values (average or weighted average, median, observed standard deviation, etc.) and a metrological background of PT schemes
are discussed. It is shown that metrological traceability, comparability, and compatibility, as well as commutability of a
reference material, are the key issues of any PT scheme that applies certified reference material as test items. Metrological
compatibility of PT results in such schemes is a property demonstrating the closeness of the PT results to the certified value
in comparison with the measurement uncertainty of their difference. The metrological background is especially important for
the selection and use of PT schemes for a limited number of participants (fewer than 30) as detailed in IUPAC/CITAC Guide
on the topic published in 2010 in Pure Appl Chem 82(5):1099–1135. 相似文献
93.
A general method has been developed for arylation of readily available 1H-perfluoroalkanes. The method employs aryl iodide and 1H-perfluoroalkane reagents, DMPU solvent, TMP(2)Zn base, and a copper chloride/phenanthroline catalyst. Preliminary mechanistic studies are reported. 相似文献
94.
Olga V. Dorofeeva Inna N. Kolesnikova Ilya I. Marochkin Oxana N. Ryzhova 《Structural chemistry》2011,22(6):1303-1314
Gas-phase enthalpies of formation of 122 relatively large organic molecules with up to 15 non-hydrogen atoms have been calculated
at the Gaussian-4 (G4) level of theory using the atomization reaction procedure. The calculated values were compared with
experimental data published mainly last years. Particular attention has been given to nitro compounds and nitrogen, oxygen,
and sulfur containing heterocyclic compounds. The expected accumulation of systematic errors as the molecular size increases
was not observed with increasing the number of non-hydrogen atoms from 6 to 15. The largest mean absolute deviation between
experimental and G4 enthalpies of formation, 10.7 kJ/mol, was revealed for nitro compounds. All theoretical values for nitro
compounds were underestimated by 5–15 kJ/mol. The best agreement with experiment with mean absolute deviation of 4.5 kJ/mol
was observed for compounds which types were widely presented in the original test set of G4 method. The mean absolute deviations
for nitrogen heterocycles (6.8 kJ/mol) and oxygen and sulfur heterocycles (9.1 kJ/mol) are noticeably larger. Experimental
enthalpies of formation of four compounds (N,N-dinitromethanamine, 2,3,5,6-tetrachloronitrobenzene, 2-methyl-2H-tetrazole, and proline) were suggested to be unreliable from comparison with the G4 values calculated from atomization energies
and isodesmic reactions. 相似文献
95.
Ioffe IN Mazaleva ON Chen C Yang S Kemnitz E Troyanov SI 《Dalton transactions (Cambridge, England : 2003)》2011,40(41):11005-11011
Chlorination of the D(2)-C(76) fullerene under various conditions is studied in detail. It is found that, in addition to the previously known C(76)Cl(18) and C(76)Cl(34), a number of intermediate chlorides are formed, with all molecules falling into two structural types. The first type is observed in the C(76)Cl(18)-C(76)Cl(28) range, whereas further chlorination provides the C(76)Cl(30)-C(76)Cl(34) compounds of the second type exhibiting a major change in the addition motif. We also present a detailed theoretical rationalization of the previously observed skeletal rearrangement in the D(2)-C(76) that affords the non-IPR (18917)C(76)Cl(24) compound. 相似文献
96.
Jagadeesan D Nasimova I Gourevich I Starodubtsev S Kumacheva E 《Macromolecular bioscience》2011,11(7):889-896
A microfluidic strategy for the encapsulation and stimulus-responsive release of molecules with distinct polarities from the interior of microgels is reported. The approach relies on (i) the generation of a primary O/W emulsion by the ultrasonication method, (ii) MF emulsification of the primary emulsion, and (iii) photopolymerization of the monomer present in the aqueous phase of the droplets, thereby transforming them into microgels. Non-polar molecules are dissolved in oil droplets embedded in the microgels. Polar molecules are physically associated with the hydrogel network. Upon heating, the microgels contract and release polar and non-polar cargo molecules. The approach paves the way for stimuli-responsive vehicles for multiple drug delivery. 相似文献
97.
Thomas Ryan Harris Michael Mazzella David Renfrew Ilya M. Spitkovsky 《Linear algebra and its applications》2011,435(11):2639-2657
The numerical range of a bounded linear operator T on a Hilbert space H is defined to be the subset W(T)={〈Tv,v〉:v∈H,∥v∥=1} of the complex plane. For operators on a finite-dimensional Hilbert space, it is known that if W(T) is a circular disk then the center of the disk must be a multiple eigenvalue of T. In particular, if T has minimal polynomial z3-1, then W(T) cannot be a circular disk. In this paper we show that this is no longer the case when H is infinite dimensional. The collection of 3×3 matrices with three-fold symmetry about the origin are also classified. 相似文献
98.
Callegari G Tyomkin I Kornev KG Neimark AV Hsieh YL 《Journal of colloid and interface science》2011,353(1):290-293
Characterization of transport and absorption properties of nanofiber webs is a challenge, because in many cases the material is soft and cannot withstand the stresses exerted by the standard instruments. In this paper, we report on development of a new technique for materials characterization. We propose to conduct wicking and permeability experiments for full characterization of the nanowebs. As an example, we used electrospun cellulose acetate nanowebs. The wicking experiments showed very good reproducibility, demonstrating the square-root-of-time dependence of wetting front position vs time. The prefactor depends on a product of capillary pressure and materials permeability. We developed a technique to independently measure the permeability of small samples of nanowebs. Wicking and permeability data allow one to estimate the pore size; SEM micrographs confirmed the obtained estimates of pore radius. In general, the proposed method allows one to characterize the transport and absorption parameters of the nanofibrous materials for which the standard procedures are inapplicable. 相似文献
99.
Diffusion rate of dye-labelled PAMAM dendrimers through free-standing silica colloidal crystals was studied as a function of the dendrimer generation and nanopore size to determine the transport selectivity. 相似文献
100.
Aharon Gero Ilya Levin 《International Journal of Mathematical Education in Science & Technology》2019,50(5):779-787
The invention of the computer has led to the establishment of a new research paradigm, computation, which has recently become more and more popular in scientific exploration. However, computation is not well represented in high school and university curricula in science and engineering, although it applies to a wide range of disciplines beyond computer science and software engineering. In light of the increasing need to provide students with computational education, this paper presents a novel way to develop computational thinking among students. The proposed approach is based on the implementation of Papert's theory of constructionism in electronic spreadsheets. In this approach, students build their knowledge while constructing the difference equation that describes a physical (or engineering) phenomenon, based on specific cases investigated in the spreadsheet. The method does not require the students to write code or perform complex calculations in the spreadsheet and makes it possible to teach advanced subjects at a relatively early stage. The method is demonstrated through contents taken from the secondary and tertiary curricula in mechanics and electromagnetism. 相似文献