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Related Concept Videos

Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

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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
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Isomerism02:43

Isomerism

22.7K
Isomers are molecules with the same molecular formula but different structural arrangements. Isomers can be further classified into constitutional isomers and stereoisomers. Constitutional isomers differ in the connectivity of their constituent atoms. For example, 2-butanol and diethyl ether are constitutional isomers, as they have the same chemical formula, C4H10O, but differ in the connectivity of the carbon and oxygen atoms. Constitutional isomers have different physical and chemical...
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Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

10.7K
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
10.7K
Disubstituted Cyclohexanes: cis-trans Isomerism02:37

Disubstituted Cyclohexanes: cis-trans Isomerism

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Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
13.7K
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

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9.4K
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
9.4K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.5K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.5K

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Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
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Photoionization of C4H5 Isomers.

S Hartweg1, J-C Loison2, S Boyé-Péronne3

  • 1Synchrotron Soleil, L'Orme des Merisiers, Gif-sur-Yvette F-91192, France.

The Journal of Physical Chemistry. A
|June 20, 2020
PubMed
Summary
This summary is machine-generated.

This study identifies three C4H5 radical isomers using coincidence spectroscopy, with their abundances varying by precursor. New insights into excited cation states and competing reaction pathways were also observed.

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Area of Science:

  • Chemical Physics
  • Molecular Spectroscopy
  • Reaction Dynamics

Background:

  • C4H5 radicals are important intermediates in combustion and atmospheric chemistry.
  • Previous studies have investigated C4H5 isomers using various spectroscopic techniques.
  • Understanding the formation and properties of C4H5 isomers is crucial for chemical kinetics.

Purpose of the Study:

  • To characterize C4H5 radical isomers produced from different C4H6 precursors.
  • To investigate the electronic states of C4H5 radicals and cations.
  • To explore competing reaction pathways in fluorine atom reactions with C4H6.

Main Methods:

  • Single-photon, photoelectron-photoion coincidence spectroscopy.
  • Mass-selected ion and slow photoelectron spectroscopy.
  • Photoelectron imaging of excited cation states.

Main Results:

  • Three C4H5 isomers were identified, with relative abundances dependent on the C4H6 precursor (1-butyne, 1,2-butadiene, 1,3-butadiene).
  • High-resolution photoelectron spectra provided new information on radical isomers and revealed autoionizing resonances of the C4H5 cation.
  • F- and H-atom addition reactions to C4H6 precursors were observed, in addition to H-atom abstraction.

Conclusions:

  • The precursor choice significantly influences the isomer distribution of C4H5 radicals.
  • Coincidence spectroscopy offers enhanced resolution for studying radical species and their excited states.
  • Fluorine atom reactions with C4H6 are complex, involving both abstraction and addition pathways.