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Updated: Jul 19, 2025

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines
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金字塔:是霍夫-勒贝尔家族的新成员

Vladimir Ya Lee1, Olga A Gapurenko2

  • 1Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571, Ibaraki, Japan. leevya@chem.tsukuba.ac.jp.

Chemical communications (Cambridge, England)
|August 8, 2023
PubMed
概括

金字塔,新的主组元素集群,呈现出独特的金字塔式碳几何. 研究人员已经成功合成和描述了稳定的金字塔,扩大了集群化学的前沿.

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VSEPR Theory and the Effect of Lone Pairs04:01

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Effect of Lone Pairs of Electrons on Molecule Geometry
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Overview of VSEPR Theory
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This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
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VSEPR Theory

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure around a central atom from an examination of the number of bonds and lone electron pairs in its Lewis structure. The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between these electron pairs by maximizing the distance between them. The electrons in the valence shell of a central atom form either bonding...
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Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
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Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?  
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
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