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Benzene at 1GHz. Magnetic field-induced fine structure
L M Heist1, C-D Poon1, E T Samulski1
1Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA.
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|July 11, 2015
Summary
Benzene-d6 deuterium NMR reveals magnetic field effects on molecular orientation. A novel method determines the sign of deuterium quadrupolar splitting, showing it aligns with magnetic field biasing in isolated molecules.
Area of Science:
- Nuclear Magnetic Resonance Spectroscopy
- Physical Chemistry
- Molecular Spectroscopy
Background:
- Deuterium NMR (2H NMR) spectroscopy is sensitive to molecular motion and orientation.
- Benzene-d6 exhibits magnetic field-induced deuterium quadrupolar splitting (Δν).
- Differences in observed Δν for central resonances and 13C satellite doublets (Δν') arise from unresolved fine structure.
Purpose of the Study:
- To investigate the origins of the difference Δ(Δν) = Δν' - Δν in benzene-d6.
- To simulate this difference and determine the relative signs of indirect coupling (JCD) and Δν.
- To understand the influence of molecular correlations on Δν in liquid benzene.
Main Methods:
- High-field deuterium NMR spectroscopy (1 GHz proton spectrometer).
- Development of pulse sequences exploiting (13)C and (2)H spectral connectivity.
- Simulation of spectral differences to analyze fine structure contributions.
Main Results:
- The difference Δ(Δν) is attributed to unresolved fine structure.
- A positive sign for Δν was determined, consistent with magnetic field biasing of isolated benzene molecules.
- Pair correlations in neat liquid benzene decrease the magnitude of Δν.
Conclusions:
- The study elucidates the factors contributing to deuterium quadrupolar splitting in benzene.
- Novel NMR techniques were employed to determine coupling constants and spectral parameters.
- Molecular orientation and intermolecular interactions significantly influence NMR observables in liquid benzene.
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