相关概念视频
01:33Radical Halogenation: Stereochemistry
Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
Halogenation to form a new chiral center:
Halogenation to form a new chiral center:
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
02:52Stereoisomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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相关实验视频
Updated: Jun 20, 2026
08:51
Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
Published on: August 18, 2017
大气中的异质立体化学.
Grace Y Stokes1, Ehow H Chen, Avram M Buchbinder
1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Journal of the American Chemical Society
|September 24, 2009
概括
立体化学显著影响大气反应. 气溶上的性有机化合物根据它们的方向与臭氧发生不同的反应,影响产品的形成,并可能使源归因成为可能.
科学领域:
- 大气化学 大气化学
- 有机地化学 有机地化学
- 化学动力学 化学动力学
背景情况:
- 许多大气中的有机化合物是性和表面活性的.
- 立体化学对大气异质氧化的影响在很大程度上仍未被探索.
- 了解这些反应对于大气模型和来源分配至关重要.
研究的目的:
- 研究立体化学在性有机分子被臭氧异质氧化中的作用.
- 量化分子导向对反应速率和产品形成的影响.
- 评估大气氧化产品中立体化学丰富的潜力.
主要方法:
- 利用非线性振动表面光谱来研究基基基基体.
- 模拟的热层条件与不同的臭氧度 (10^11到10^13分子/厘米^3) 在1 atm的.
- 进行了动力学研究,以确定异质的臭氧分解速率常数.
主要成果:
- 具有向气相方向的反应性C=C键的二聚体与臭氧反应速度快2倍.
- 观察到的反应速率的差异表明立体化学影响异质臭氧分解.
- 确定了氧化产品 (气体或表面结合) 的立体化学丰富潜力.
结论:
- 分子立体化学和导向是性有机气溶与臭氧异质反应的关键因素.
- 在臭氧溶解过程中的动态分辨率可以导致立体化学丰富的产品.
- 这些发现对了解大气过程,前生物化学和识别排放源有影响.