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苯取代定位效应的量子化学研究 总被引:3,自引:1,他引:3
采用RHF/6-31G(d)方法优化分子构型,在此基础上研究取代定位效应,对14种苯的取代物进行了苯环上C原子所带总电荷量的计算,给出一个直观的苯的取代定位和活化(钝化)作用的判断标准.此法对芳基亲电取代反应有一定的预见性. 相似文献
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芳杂环的亲电取代活性及定位效应是许多理论研究的对象。研究的重点多是同系物间的活性比较及分子内的取代定位效应。其规律往往用反应活性部位的电荷数量及分布来解释。量子化学计算结果,一般也符合物理有机的这一传统解释。因此,电荷数量及分布决定分子的取代活性及定位仍是有机化学中普遍接受的观点[1]。不少量子化学活性指标也用于亲电取代活性及定位效应的解释,但一般只局限于同系物的比较,不同母核的芳杂环的亲电取代活性比较则较少为人们所注意。 相似文献
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自1895年Holleman总结出亲电芳香取代定位规律之后,根据大量事实,人们对苯的一取代所引起的亲电取代反应有所认识,把取代基分为邻对位定位基(即第一类定位基)和间位定位基(即第二类定位基),并对定位基使新导入基团定位的情况也有所了解。如何判断苯环上原有取代基属于哪一类定位基,已有不少定性的经验规律。一元取代苯的再取代,苯环上原有基团的定位能力往往取决于这个定位基对苯环π_6~6环状共轭体系的贡献大 相似文献
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研究了一种基于Friedel-Crafts亲电取代的新型缩聚反应,反应基团是氮原子的苯对位氢原子和芴醇上的羟基,氮原子的富电子效应活化了苯对位氢原子的亲电取代能力,同时芴醇(似三苯甲醇结构)是高活性的烷基化试剂,使得小分子亲电取代反应可扩展为高分子缩聚反应.探索了两种缩合途径,"A-A,B-B"型共缩聚和"A-B"型自缩聚.4,4′-双(苯基-对甲苯基氨基)联苯(TPD)与芴醇共缩聚,得到数均分子量为1·5×104~2·0×104的共聚物,而芴醇的自缩聚,可得到单分散、立体环状结构的3聚体. 相似文献
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~(13)C-NMR谱的化学位移与芳烃亲电取代定位效应 总被引:1,自引:0,他引:1
在芳烃亲电取代反应中,取代基的定位效应问题是有机化学工作者所普遍关心的。从本世纪初期就开始研究苯环上取代基对芳烃亲电取代反应的影响因素。根据亲电取代反应中取代产物的比例关系,归纳出苯环上不同取代基定位能力的相对强弱序列。此序列定性地解释了许多简单的芳烃亲电取代反应的事 相似文献
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在芳烃亲电取代反应中,取代基的定位效应是有机化学工作者普遍关心的问题。从本世纪初就开始研究苯环上取代基对芳烃亲电取代反应定位效应的影响,根据反应中取代产物的 相似文献
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苯的一取代物所起的亲电取代反应,根据大量实验事实归纳出下面的定位规律: 1.在苯环上新导入的取代基的位置主要由原有取代基来决定。2.可以把取代基分为两类:第一类取代基使新导入的基团进入邻位和对位,并且使反应易于进行(卤素除外);第二类定位基使新导入的取代基进入间位,并且使取代反应难于进行。 相似文献
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蒋锡夔研究员是我国物理有机化学和有机氟化学的主要奠基人。本文首先介绍蒋锡夔研究员的科学经历,然后介绍他在不同时期取得的代表性科学成就,主要包括有关四氟乙烯的亲电加成反应,氟橡胶研究,亲卤反应,自由基化学及有机分子的簇集与自卷等方面的研究。 相似文献
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亲电取代反应是一类基本的有机反应,其中以苯环上的亲电取代反应最常见。该反应的反应活性及反应的位点与苯环上已有的取代基有很大的关系。本文从波谱学的角度,利用核磁数据,阐述了已有的取代基如何影响苯环的电子云密度,进而影响苯环亲电取代反应的活性和取代的位置。本文视角新颖,将对学生的学习及科研产生启发。 相似文献
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用分子轨道来描述有机反应的过程对于正确理解有机反应的机理非常重要,分子轨道可以清楚地描述出反应的选择性和立体化学等信息。本文讨论了脂肪和芳香亲核取代、芳香亲电取代、加成和消除等几种经典有机化学反应过程的分子轨道描述。 相似文献
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Paul T. Nyffeler Sergio Gonzalez Durn Michael D. Burkart Stphane P. Vincent Chi‐Huey Wong 《Angewandte Chemie (International ed. in English)》2005,44(2):192-212
The replacement of hydrogen atoms with fluorine substituents in organic substrates is of great interest in synthetic chemistry because of the strong electronegativity of fluorine and relatively small steric footprint of fluorine atoms. Many sources of nucleophilic fluorine are available for the derivatization of organic molecules under acidic, basic, and neutral conditions. However, electrophilic fluorination has historically required molecular fluorine, whose notorious toxicity and explosive tendencies limit its application in research. The necessity for an electrophilic fluorination reagent that is safe, stable, highly reactive, and amenable to industrial production as an alternative to very hazardous molecular fluorine was the inspiration for the discovery of selectfluor. This reagent is not only one of the most reactive electrophilic fluorinating reagents available, but it is also safe, nontoxic, and easy to handle. In this Review we document the many applications of selectfluor and discuss possible mechanistic pathways for its reaction. 相似文献
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Nyffeler PT Durón SG Burkart MD Vincent SP Wong CH 《Angewandte Chemie (International ed. in English)》2004,44(2):192-212
The replacement of hydrogen atoms with fluorine substituents in organic substrates is of great interest in synthetic chemistry because of the strong electronegativity of fluorine and relatively small steric footprint of fluorine atoms. Many sources of nucleophilic fluorine are available for the derivatization of organic molecules under acidic, basic, and neutral conditions. However, electrophilic fluorination has historically required molecular fluorine, whose notorious toxicity and explosive tendencies limit its application in research. The necessity for an electrophilic fluorination reagent that is safe, stable, highly reactive, and amenable to industrial production as an alternative to very hazardous molecular fluorine was the inspiration for the discovery of selectfluor. This reagent is not only one of the most reactive electrophilic fluorinating reagents available, but it is also safe, nontoxic, and easy to handle. In this Review we document the many applications of selectfluor and discuss possible mechanistic pathways for its reaction. 相似文献
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Hennrich G Lynch VM Anslyn EV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(10):2274-2278
The conversion of 1,3,5-substituted benzene and mesitylene by electrophilic aromatic substitution and Sonogashira cross-coupling, respectively, furnished the C3-symmetric, hexasubstituted benzene derivatives 1 and 2 with an alternating substitution pattern. Based on the molecular scaffolds obtained, the two systems serve as model compounds for novel receptor molecules with distinct geometric features. X-ray structures have been obtained for 1 and 2, which are discussed in regard to their aptitude as receptor platforms or supramolecular building blocks. By looking at the rotational barriers for the functional groups placed around the molecular scaffolds by variable temperature 1H NMR spectroscopy, 1 and 2 turn out to exist in rapidly interconverting conformations. The alignment of these potential binding groups around the molecular scaffolds should be strongly biased by specific interactions with suitable guest molecules. 相似文献
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IntroductionThestudiesonconductivepo1ymershavebeenofmuchinterestsbothinex-perimentalworkandtheorysincetheresultsonconductivityofdopedpolyacety-lenewerereported.Itwasreportedthatthehighestconductivityofdopedpoly-acetylenereachedupto1O5s/cmandjustfellintherangeofmetalconduction[1].Somepeoplehaveputforwardone-dimension(1D)graphitematerialfamilytobeconsistedofcondensedaromaticrings.Therearetwbkindsofimportantmolecularskeletonsforms,oneisanextended.versionfrompolyacene.Thepolyacenecanbeobtaintedb… 相似文献
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James J. Palesch Beau C. Gilles Jared Chycota Moriana K. Haj Grant W. Fahnhorst 《Green Chemistry Letters and Reviews》2019,12(2):117-126
ABSTRACTA two-step synthetic sequence was developed for the undergraduate organic chemistry laboratory using vanillin as the starting material. The multi-step synthesis was designed to replace two traditional experiments teaching electrophilic aromatic substitution and carbon–carbon bond forming chemistries with greener transformations. Vanillin is iodinated using Oxone® and potassium iodide in refluxing water, and students are tasked with determining the position of aromatic substitution using 1H NMR spectroscopy. The tan, shiny, pleasant-smelling iodovanillin is subsequently used in an aqueous Suzuki-Miyaura reaction with para-methylphenylboronic acid; strategically chosen to afford a second instructive 1H NMR spectrum. Both conventional heating and microwave conditions can be employed for the palladium-catalyzed reaction. This synthetic sequence, successfully performed over multiple semesters by hundreds of students, models green chemistry principles through the use of a potentially renewable feedstock and safer reagents, the choice of water as a safer reaction solvent, and the employment of a catalytic reaction. Additionally, the sequence minimizes waste in teaching labs through use of an intermediate product. 相似文献
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Xie SY Peng Y Chen M Huang RB Chow YL Zheng LS 《The Journal of organic chemistry》2005,70(4):1400-1407
[reaction: see text] The forced one-electron reduction of carbon tetrachloride with sodium in a sealed steel vessel is shown to have a narrow window of conditions to arrest the reaction at the polychlorinated aromatic hydrocarbons (PCAHs), as well as to prevent the reaction from proceeding all the way to the final stage of graphite and other carbon solids. The intermediates are quenched with toluene or benzene to give electrophilic substitution products and with water to give a quinomethine as the major product. The product pattern leads us to propose the carbene, perchlorobenzo[c,d]pyren-6-ylidene, or its reversible dimer as the major intermediate among others, that survives the severe conditions until coming into contact with these nucleophiles. Mainly from aromatic resonance stabilization, the carbene is proposed to have a delocalized singlet state analogous to a ylide electronic structure and, thus, undergoes observed ionic reactions instead of typical carbene reactions. This work serves as a mechanistic link on the structural evolution of carbon networks between molecular chemistry and nanomaterial chemistry. 相似文献