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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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Updated: Jun 20, 2026
08:51
Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
Published on: August 18, 2017
大気の異質なステレオ化学.
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
まとめ
ステレオ化学は,大気反応に大きな影響を与えます. エアロゾール上のキラル有機化合物は,その方向性によってオゾンと異なった反応し,製品形成に影響を与え,潜在的に源の属性を可能にします.
科学分野:
- 大気化学 大気化学
- オーガニック・ジオケミストリー オーガニック・ジオケミストリー
- 化学動力学 化学動力学
背景:
- 大気中の多くの有機化合物はキラルであり,表面活性である.
- 立体化学が大気中の異質な酸化に及ぼす影響は,まだほとんど未調査のままである.
- これらの反応を理解することは,大気モデリングと源の配分に不可欠です.
研究 の 目的:
- キラルな有機分子のオゾンによる異質的酸化における立体化学の役割を調査する.
- 分子指向が反応速度や産物形成に及ぼす影響を定量化するために.
- 大気中の酸化産物におけるステレオ化学的濃縮の可能性を評価する.
主な方法:
- 非線形振動表面スペクトロスコピーを活用して,シリカ基板上のキヌクリジンダイアステロエーマーを研究しました.
- 1 atmのヘリウムで異なるオゾン濃度 (10^11から10^13分子/cm^3) を有するシミュレートされたトロポスフィアの条件.
- 異質なオゾノリシス速度の定数を決定するために運動学的研究を行った.
主要な成果:
- 反応性C=C結合がガス相に向いているダイアステロエーマーがオゾンと2倍速く反応した.
- 反応速度における観察された差異は,ステレオ化学が異質なオゾノリシスに影響することを示唆しています.
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結論:
- 分子立体化学と方向性は,キラルな有機気溶液とオゾンとの異質な反応における重要な要因である.
- オゾノリシス中の運動解像度は,ステレオ化学的に濃縮された製品につながる可能性があります.
- これらの発見は,大気中のプロセス,プレバイオティクスの化学,および排出源の特定を理解するための意味を持っています.