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Relative Stabilities of Alkenes01:59

Relative Stabilities of Alkenes

13.8K
The relative stability of alkenes can be determined by comparing their heats of hydrogenation. The lower heat of hydrogenation indicates the more stable alkene.  The three main factors determining the relative stability of alkenes are i) the number of substituents attached to the double-bond carbon atoms, ii) hyperconjugation, and iii) the stereochemistry of the double bond.
13.8K
Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes02:14

Combustion Energy: A Measure of Stability in Alkanes and Cycloalkanes

6.2K
The low reactivity in alkanes can be attributed to the non-polar nature of C–C and C–H σ bonds. Alkanes, therefore, were  initially termed as “paraffins,” derived from the Latin words: parum, meaning “too little,” and affinis, meaning “affinity.”
Alkanes undergo combustion in the presence of excess oxygen and high-temperature conditions to give carbon dioxide and water. A combustion reaction is the energy source in natural gas, liquified...
6.2K
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

1.9K
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
1.9K
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

13.9K
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
13.9K
Structure and Bonding of Alkenes02:47

Structure and Bonding of Alkenes

16.0K
Olefins, which are unsaturated hydrocarbons containing one or more carbon–carbon double bonds, are broadly divided into alkenes and cycloalkenes. The general chemical formula of an alkene is CnH2n.
Doubly bonded carbons are sp2 hybridized and have a trigonal planar geometry. The double bond is composed of a σ bond formed by the overlap of hybrid orbitals and a π bond produced by the lateral overlap of unhybridized 2p orbitals on both the carbons. Each carbon atom is...
16.0K
Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

12.4K
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
12.4K

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Updated: Jun 7, 2025

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
10:44

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Published on: April 19, 2019

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超稳定基:它们是否非常不反应?

Matthew D Summersgill1, Lawrence R Gahan1, Sharon Chow1

  • 1School of Chemistry and Molecular Biosciences, University of Queensland Brisbane 4072 Queensland Australia c.williams3@uq.edu.au.

Chemical science
|November 21, 2024
PubMed
概括

研究人员合成了四种超稳定基,通过发现意想不到的氧化敏感性,挑战了它们预测的不反应性. 这项工作设定了一个新的基准,并强调需要精细化超稳定分子的定义.

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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators
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Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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科学领域:

  • 有机化学 有机化学
  • 计算化学的计算化学
  • 化学合成 化学合成

背景情况:

  • 1981年,超稳定基因在理论上被预测是非常不反应的.
  • 自最初识别以来,只有三个这样的系统被实验报告.
  • 理论预测完全依赖于计算方法.

研究的目的:

  • 报道了四种超稳定基的新的一合成.
  • 为了研究这些合成的超稳定基的反应性.
  • 解决理论预测和实验观测之间的差异.

主要方法:

  • 采用了一,望远镜合成方法.
  • 合成了四种新的超稳定烯化合物.
  • 对合成的化合物进行了反应性研究,包括氧化.

主要成果:

  • 已经成功合成了四种超稳定的基.
  • 在这些化合物中观察到对氧化的意想不到的反应性.
  • 这些发现挑战了长期以来关于显著无反应性的假设.

结论:

  • 这项研究为高稳定性烯合成建立了新的基准.
  • 观察到的反应性需要重新评估基的超稳定性定义.
  • 需要进一步的研究来协调实验发现与初始计算预测.