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991.
Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide,Formaldehyde, and Sodium Hydroxide 下载免费PDF全文
Robert Czochara Prof. Grzegorz Litwinienko Dr. Hans‐Gert Korth Dr. Keith U. Ingold 《Angewandte Chemie (International ed. in English)》2018,57(29):9146-9149
In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH2OOCH2OH, is the intermediate, which decomposes to yield H2 and formate, proposing a mechanism that would nowadays be considered as a “concerted process”. Since then, several other (conflicting) “mechanisms” have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base‐dependent reaction, both H atoms of H2 derive from the CH2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH2OOCH2OH or from water. Quantum‐chemical CBS‐QB3 and W1BD computations show that H2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH2OOCH2OH, thereby ruling out a free radical pathway. 相似文献
992.
The present study reports the first phytochemical investigation of the seed kernels of Manilkara bidentata (Balata) harvested in Trinidad, W.I. Gas chromatography–mass spectrometry (GC-MS) analysis of the n-hexane, chloroform, ethyl acetate, ethanol and methanol extracts showed a total of 39 components. 2,6,10,14,18-pentamethyl-2,6,10,14,18-eicosapentaene (74.93%), 9-octadecenoic acid, (Z)- 2,3-dihydroxypropyl ester (79.98%), (Z)-ethyl oleate (92.75%), Z,E-2-methyl-3,13-octadecadien-1-ol (80.51%) and 5-(hydroxymethyl)-2-furancarboxyaldehyde (50.32%) were the major constituents identified in the n-hexane, chloroform, ethyl acetate, ethanol and methanol extracts, respectively. The extracts showed the presence of several bioactive components and provides reference data for further research of its active constituents. 相似文献
993.
Sateesh Kumar Arepalli Yunseon Choi Kiho Lee Jong-Soon Kang Jae-Kyung Jung Heesoon Lee 《Tetrahedron》2018,74(14):1646-1654
An efficient, transition-metal-free cascade synthetic method has been developed for new 2-aryl/heteroaryl sulfonated benzo[f][1,7]naphthyridines. It is tert-butyl hydroperoxide (TBHP) mediated highly regioselective sulfonylation?cyclization?aromatization process between N-(3-aryl/heteroarylprop-2-yn-1-yl)quinolin-3-amines and aryl/heteroaryl sulfonylhydrazides. This synthetic protocol offers one-step strategy for CS and CC bond formations with a broad range of functional group tolerance. It is a simple, mild, and atom-economical route for the synthesis of various valuable functionalized 1, 2-aryl/heteroaryl sulfonated benzo[f][1,7]naphthyridines in moderate yields. Since the core motif of 2-sulfonated benzo[f][1,7]naphthyridines are biologically and pharmaceutically important (TLR activity 7, 8 modulators). Additionally, the synthesized derivatives were evaluated for their in vitro cytotoxic activities against six human cancer cell lines including lung (NCIH23), colon (HCT15), gastric (NUCG-3), renal (ACHN), prostate (PC-3), and breast (MDA-MB-231) cell lines. These compounds displayed significant cytotoxic activities against all tested human cancer cell lines. 相似文献
994.
Jana L. Markley Tyler L. Morse Nigam P. Rath Timothy A. Wencewicz 《Tetrahedron》2018,74(22):2743-2753
A photochemical approach to 3-phenyl-3-hydroxy-β-lactams (3-HβLs) is reported. Irradiation of aryl-β-ketoformamides with a UV light band centered at 300?nm provides the corresponding 3-aryl-3-HβLs with good conversion. The scope of the photocyclization is explored with an electronically diverse panel of substrates that provides mechanistic insight supporting a Norrish-Yang type II cyclization. A flexible synthetic route to phenyl-β-ketoformamides, followed by photoirradiation, allows for efficient incorporation of the β-lactam pharmacophore into aromatic organic scaffolds. Taken collectively, the improved and optimized synthetic route to provide both β-ketoformamides and 3-HβLs—in combination with the expanded analysis of substrate scope and limitations—reported herein will serve as a necessary reference for the direct, atom-economical, radical-mediated installation of 3-HβL scaffolds en route to the generation of other biologically active small molecules. 相似文献
995.
A singular integral operator with rough kernel 总被引:3,自引:0,他引:3
Let be a bounded radial function and an function on the unit sphere satisfying the mean zero property. Under certain growth conditions on , we prove that the singular integral operator
is bounded in for .
996.
Saburou Saitoh 《Proceedings of the American Mathematical Society》1997,125(12):3633-3639
Let be an arbitrary map from an abstract set into an abstract set . We shall use the theory of reproducing kernels to provide a general method for representing the inverse map in terms of . We give several concrete examples of this method.
997.
Zeta Function on a Generalised Cone 总被引:2,自引:0,他引:2
The analytic properties of the -function for a Laplace operator on a generalised cone
are studied in some detail using Cheeger's approach and explicit expressions are given. In the compact case, the -function of the Laplace operator turns out to be singular at the origin. As a result, strictly speaking, the -function regularisation does not regularise and a further subtraction is required for the related one-loop effective potential. 相似文献
998.
999.
Every translation invariant positive definite Hermitian bilinear functional on the Gel'fand-Shilov space sMpMp(n×nK) of general type S is of the form B(,) = (x)(x)d(x), , sMpMp (n), where is a positive {M}-tempered measure, i.e., for every > 0 exp[-M(|x|)] d(x) < . To prove this we prove Schwartz kernel theorem for {M}-tempered ultradistributions and need Bochner-Schwartz theorem for {M}-tempered ultradistributions. Our result includes most of the quasianalytic cases. Also, we obtain parallel results for the case of Beurling type (Mp. 相似文献
1000.
After the appearance of W. Arendt's result that “Gaussian estimate of a semigroup implies the Lp-spectral independence of the generator,” various generalizations have been obtained. This paper shows that a certain kernel estimate of a semigroup implies the Lp-spectral independence of the generator, generalizing the case of upper Gaussian estimate and “Gaussian estimate of order α(0,1] [S. Miyajima, H. Shindoh, Gaussian estimates of order α and Lp-spectral independence of generators of C0-semigroups, Positivity 11 (1) (2007) 15–39], Definition 3.1.” The proof uses S. Karrmann's result about the Lp-spectral independence and B.A. Barnes' theorem about the spectrum of integral operators. As an application, the Lp-spectral independence of −[(−Δ)α+V] (α(0,1]) for a suitable V is proved with the help of a recent result by V. Liskevich, H. Vogt and J. Voigt [V. Liskevich, H. Vogt, J. Voigt, Gaussian bounds for propagators perturbed by potentials, J. Funct. Anal. 238 (2006) 245–277]. 相似文献