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排序方式: 共有226条查询结果,搜索用时 15 毫秒
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The mass spectra of eleven 1,2,4-triazepines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Each of the five structures of the triazepine ring present is characterized by a particular group of fragmentations. 相似文献
4.
Structural and magnetic properties of iron(II) complexes with 1,4,5,8,9,12-hexaazatriphenylene (HAT)
Shatruk M Chouai A Prosvirin AV Dunbar KR 《Dalton transactions (Cambridge, England : 2003)》2005,(11):1897-1902
Reactions of Fe(II) salts with the ligand 1,4,5,8,9,12-hexaazatriphenylene (HAT) led to the isolation and characterization of four new compounds: [Fe3(HAT)(H2O)12](SO4)3.3.3H2O (1), [Fe2(HAT)(SO4)(H2O)5](SO4).2H2O.CH3OH (2), [Fe2(HAT)(SO4)(H2O)5](SO4).3H2O (3), and [Fe3Cl5(HAT)(CH3OH)4(H2O)]Cl (4). Compound 1 crystallizes as a trinuclear cluster in which HAT acts as a tris-chelating ligand. Compounds 2 and 3 are two polymorphs of an infinite one-dimensional structure in which the Fe atoms are coordinated to HAT and then connected into the chain through bridging sulfate anions. Compound 4 exhibits a similar chain structure, but with bridging chloride ligands. The magnetic behavior of the new compounds is indicative of weak antiferromagnetic coupling between the Fe(II) centers through the HAT ligand. 相似文献
5.
Sarah Almazroa Mohamed H. Elnagdi Abdellatif M. Salah El‐Din 《Journal of heterocyclic chemistry》2004,41(2):267-272
The enaminones 1b,d,f react with 4‐phenyl‐3‐methyl‐5‐pyrazoleamine 3a to yield the pyrazole derivatives 4a‐c that cyclised readily on reflux in pyridine solution in presence of hydrochloric acid to yield the pyrazolo[1,5‐a]pyrimidines 5a‐c. Similarly 3(5)‐amino‐1H‐triazole (3b) reacted with 1b,d,f to yield the triazolo[1,5‐a]pyrimidines 5d‐f. In contrast attempted condensation of the 5‐tetrazoloamine (3c) with 1a,d,e resulted in its trimerisation and only triaroylbenzene 8a,d,e was isolated. The reaction of 1a,b,d with anthranilonitrile 9a and the reaction of 1a‐c with the 2‐aminocyclohexene thiophene‐3‐nitrile 10a afforded the cis enaminones 11a‐c and 12a‐c. Similarly, reaction of 1a‐c with the methylanthranilate 9b and reaction of 1b,e with ethyl 2‐aminocyclohexene thiophene‐3‐carboxylate 10b afforded the cis enaminones 11d‐f and 12d,e respectively. Attempted cyclization of 11a‐c into quinoline failed. Successful cyclization of 11d into the quinolinone 13 could be affected, on heating for five minutes in a domestic microwave oven at full power. The reaction of 1a‐c,f with piperidine afforded the trans enaminones 14a‐d. Similarly, trans 14e was formed from the reaction of 1b with morpholine. The coupling reaction of 1b with excess of benzene diazonium chloride afforded the formazane 16. The enaminone 2 reacted with heterocyclic amines to yield the pyridones 17,18. 相似文献
6.
We report here a one-step synthesis of the 4,5,6,7-tetrahydro-1H- 1,2,4,-triazolo[4,3-d][1,4]diazepine, 4-6, and 1,2,4-oxadiazolo[4,5-d][1,4]-diazepine, 7-10, by 1,3-dipolar cycloaddition of nitrile imines and nitrile oxides with 2,3-dihydro-H-1,4-diazepine, 1. In all cases these cycloaddition are peri- and regioselectives (the C ? N bond is sole affected) and occures with high yields. Structure and conformations of cycloadducts have been assigned by means of nmr analysis 相似文献
7.
Abdellatif Kamal El Bouâzzaoui Choubabi Ahmed Jellal 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(5):91
We study the electronic band structures of massless Dirac fermions in symmetrical graphene superlattice with cells of three regions. opening gaps and additional Dirac points. Finally, we inspect the potential effect on minibands, the anisotropy of group velocity and the energy bands contours near Dirac points. We also discuss the evolution of gap edges and cutoff region near the vertical Dirac points. 相似文献
8.
In this paper, using the penalty method in conjunction with graph-convergence, we study the existence of solutions for a class
of generalized variational inequalities with variational problem constraints. Our results extend, improve and develop some
known results in this field. Our method of proofs is very simple and does not use the hemicontinuity nor the pseudo-continuity
properties of monotone operators. 相似文献
9.
We introduce a method for change detection under nonuniform changes of intensity using an improved least-squares method. A locally adaptive normalizing window is correlated with the two images, and a morphological postprocessing is then applied to isolate objects that have been added or removed from the scene. We use a modification of the least-squares solution to get rid of clutter caused by intensity changes that do not satisfy the model assumed for the least-squares solution. 相似文献
10.
A posteriori error analysis for nonconforming approximations of an anisotropic elliptic problem 下载免费PDF全文
Boujemâa Achchab Abdellatif Agouzal Adil Majdoubi Driss Meskine Ali Souissi 《Numerical Methods for Partial Differential Equations》2015,31(3):950-976
We develop in this article an a posteriori error estimator for the P1‐nonconforming finite element approximation, for a diffusion‐reaction equation. We adopt the error in a constitutive law approach in two and three dimensional space, for not necessary piecewise constant data of problems. The efficiency and the reliability of our estimators are proved, neither Helmholtz decomposition of the error nor saturation assumption. The constants are explicitly given, which prove the robustness of these estimators. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 950–976, 2015 相似文献