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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.
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¹H NMR: Complex Splitting01:13

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Radicals: Electronic Structure and Geometry01:07

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¹H NMR: Long-Range Coupling01:27

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Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
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Hyperfine coupling in methyl radical isotopomers.

Iain McKenzie1, Jean-Claude Brodovitch, Khashayar Ghandi

  • 1Department of Chemistry and TRIUMF, Simon Fraser University, 8888 University Drive, Burnaby, B.C. V5A 1S6, Canada.

The Journal of Physical Chemistry. A
|October 6, 2007
PubMed
Summary

Hyperfine coupling constants of muoniated methyl radicals (CH2Mu, CD2Mu) were measured. Unlike regular methyl radicals, their coupling constants increase with temperature due to solvent effects on bending modes.

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Area of Science:

  • Physical Chemistry
  • Chemical Physics
  • Spectroscopy

Background:

  • Methyl radicals (CH3, CD3) exhibit temperature-dependent hyperfine coupling constants (hfcs).
  • Muoniated methyl radicals (CH2Mu, CD2Mu) offer unique insights into radical dynamics due to the light mass of muonium.

Purpose of the Study:

  • To measure the temperature dependence of hfcs for CH2Mu and CD2Mu.
  • To investigate the influence of solvent and isotopic mass on radical bending modes and hfcs.

Main Methods:

  • Muon spin spectroscopy was used to measure hfcs of CH2Mu and CD2Mu radicals.
  • Radicals were generated in ketene and ketene-d2 over a wide temperature range.

Main Results:

  • Muoniated methyl radicals showed larger hfcs than CH3 and CD3 due to increased zero-point energy in out-of-plane bending.
  • Negative hfcs of muoniated radicals increased in magnitude with temperature, unlike CH3/CD3.
  • This behavior was attributed to solvent-induced changes in the bending force constant, dominating over vibrational excitation.

Conclusions:

  • Solvent effects significantly influence the out-of-plane bending mode of muoniated methyl radicals.
  • The contrasting temperature dependence of hfcs between muoniated and non-muoniated methyl radicals highlights the interplay of mass, vibrational frequency, and solvent interactions.