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1.
分离出环膦二肽的几何异构体。用高分辩~H NMR结合其它光谱确定了异构体的数目,用X射线确定了它们的立体结构,发现磷上苯环与其α-碳上取代基互为顺式,六元环采用扭船式构象。 相似文献
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一、问题的提出环己烷有多少种构象异构体?它们的比例是多少?这个问题在国内目前的教科书中,不尽一致.在一些教材中,仍仅着眼于键角张力的影响.认为仅有两种极限构象,一种叫“椅式”,另一种叫“船式”.它不仅忽略了扭船式(twist),而且“极端”的提法也不准确,因为在能量-构象转变座标图上,它们并不处于两个极端,扭船式也不应看做是船式和椅式之间的过渡状态.关于各种构象在室温下的比例,说法有:船式:椅式=1∶1000,扭船式:椅式=1∶1000,扭船式:椅式=1∶10000等.本文想就究竟环己烷有几种异构体,在室温下,它们的比 相似文献
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从头计算法研究沙蚕毒和杀虫环分子的几何构型与电子结构 总被引:1,自引:1,他引:0
用Hartree-Fock/6-31G*从头算确定了沙蚕毒和杀虫环分子的几何构型,在全局优化中发现杀虫环分子的椅式和船式两种稳定构象,在二级Moller-plesset微扰理论MP2/6-31*水平下,椅式较船式稳定27.06kJ/mol.用MP2/6-31G*波函数计算电子相关校正的分子静电势,以此为基础讨论生物活性与静电势的关系。发现对此二分子,Mulliken布居分析获得的原子净电荷存在问题,本文用Breneman提出的从静电势导出原子净电荷的CHELPG方法计算了原子净电荷。 相似文献
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用单晶X射线衍射方法测定了6-苯甲酰基-5-(邻氯苯基)-2,3,3a,4,5,6-六氢-3a-苯基-(1,2,3-三乙酸乙酯基)-1H-吡咯啉[1,2-a][1,5-]苯并二氮杂的晶体结构.单斜晶系,空间群P2_1/c,a=1.3235(5)nm,b=1.7142(6)nm,c=1.6204(6)nm,β=100.49(3)°,Z=4,最终偏离因子R=0.062,R_w=0.075.晶体结构测定结果表明分子中二氮杂七元环采取船式构象,动力学模拟退火计算结果的最低能量构象为椅式,两者的能量差不大,表明这种船式椅式的变化是非常容易发生的. 相似文献
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结合环己烷的构象与能量关系,讨论[3,3]σ迁移反应的立体化学过程。[3,3]σ迁移反应生成的主产物经过的是椅式过渡态,生成的次要产物经过的是扭船式过渡态,而不是以前认为的船式过渡态。 相似文献
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用PM3分子轨道方法研究了α-环糊精的包合作用对环己烷构象平衡的影响。发现α-环糊精的包合作用可以改变环己烷的构象平衡。计算结果表明,虽然环己烷的椅式构象比船式构象稳定18.5 kJ*mol-1, 但在α-环糊精的包合物中,船式环己烷包合物比椅式环己烷包合物稳定4.4 kJ*mol-1。因此,超分子体系中客体分子的构象平衡不能简单地从其游离态的构象平衡外推得到,而应该考虑在超分子体系中分子间相互作用对构象的影响。 相似文献
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用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%. 相似文献
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Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction
Laurent Gavara Thomas Boisse Jean-Pierre Hénichart Adam Daïch Philippe Gautret 《Tetrahedron》2010,66(38):7544-5571
In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments. 相似文献
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Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields. 相似文献
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The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula. 相似文献
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Rebecca J. Burton Mandy L. CrowtherNeal J. Fazakerley Shaun M. FilleryBarry M. Hayter Jason G. KettleCaroline A. McMillan Paula PerkinsPeter Robins Peter M. SmithEmma J. Williams Gail L. Wrigley 《Tetrahedron letters》2013
The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines. 相似文献
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KMnO4-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields. 相似文献
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N. A. Nedolya 《Chemistry of Heterocyclic Compounds》2008,44(10):1165-1219
The review contains a concise historical account and information on the most significant researches undertaken by the staff
at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry
of Heterocyclic Compounds.
Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008. 相似文献
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Regiospecific and direct imidation of the methyl C(sp3)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products. 相似文献
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A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL. 相似文献
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A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions. 相似文献