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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Chain Reactions01:29

Chain Reactions

Chain reactions involve highly reactive transient species, such as atoms or free radicals, as intermediates. These intermediates facilitate rapid reactions over an extended period. The process includes a series of steps: a reactive intermediate is consumed, reactants are converted to products, and the intermediate is regenerated. This cycle enables continuous repetition, amplifying the production of products with a small amount of intermediate. Chain reactions often utilize free radicals as...
Mass Spectrometry: Alkyl Halide Fragmentation01:22

Mass Spectrometry: Alkyl Halide Fragmentation

Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides typically produces two distinct molecular ion peaks, the molecular ion peak, [M], and the molecular ion plus two, [M + 2] peak. The relative heights of these two peaks are proportional to the isotopic abundance ratios of the halide. For example, 2‐chloropropane and 1‐bromopropane display two peaks with relative peak heights in a 3:1 and 1:1...
NMR Spectroscopy of Benzene Derivatives01:37

NMR Spectroscopy of Benzene Derivatives

Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling constants depend...
Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene01:17

Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene

The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.

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Updated: Jun 24, 2026

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
08:51

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Published on: August 18, 2017

Multiphoton dissociation dynamics of CH3Br.

Fengyan Wang1, M Laura Lipciuc, Xueming Yang

  • 1State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, PRChina.

Physical Chemistry Chemical Physics : PCCP
|March 24, 2009
PubMed
Summary

State-resolved photodissociation of methyl bromide cations (CH3Br+) was investigated. The study reveals significant excitation in the umbrella mode of the methyl cation fragment, particularly when producing the spin-orbit excited bromine atom.

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Last Updated: Jun 24, 2026

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Area of Science:

  • Physical Chemistry
  • Chemical Physics
  • Molecular Dynamics

Background:

  • Understanding molecular photodissociation dynamics is crucial for various chemical processes.
  • Methyl bromide (CH3Br) is a molecule of interest due to its atmospheric relevance and simple structure.
  • Previous studies on CH3Br photodissociation have provided foundational insights into its fragmentation pathways.

Purpose of the Study:

  • To investigate the state-resolved photodissociation dynamics of methyl bromide cations (CH3Br+).
  • To elucidate the influence of electronic states and vibrational excitation on the dissociation mechanisms.
  • To analyze the product state distributions and fragment angular distributions to understand dissociation pathways.

Main Methods:

  • Utilized a combination of slice imaging and velocity mapping techniques.
  • Prepared parent CH3Br+ ions via (2 + 1) two-photon resonant three-photon ionization through the 5s Rydberg state.
  • Analyzed photoelectron spectra to determine the initial electronic and vibrational states of CH3Br+.

Main Results:

  • CH3Br+ ions were produced in the spin-orbit ground electronic state with significant vibrational excitation.
  • Photodissociation yields CH3+ and Br atoms, with substantial excitation observed in the umbrella mode of CH3+.
  • Distinct dissociation mechanisms were identified for the Br(2P(1/2)) and Br(2P(3/2)) atomic bromine channels, evidenced by fragment angular distributions.

Conclusions:

  • The photodissociation of CH3Br+ exhibits complex dynamics influenced by vibrational and electronic states.
  • Excitation of the umbrella mode in CH3+ is particularly pronounced when forming spin-orbit excited Br atoms.
  • The study provides detailed insights into the state-resolved fragmentation pathways of methyl bromide cations.