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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.
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...

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Nuclear Magnetic Resonance Spectroscopy for the Identification of Multiple Phosphorylations of Intrinsically Disordered Proteins
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Nuclear Magnetic Resonance Spectroscopy for the Identification of Multiple Phosphorylations of Intrinsically Disordered Proteins

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Separate-local-field NMR spectroscopy on half-integer quadrupolar nuclei.

Julia Grinshtein1, Christopher V Grant, Lucio Frydman

  • 1Department of Chemical Physics, Weizmann Institute of Sciences, 76100 Rehovot, Israel.

Journal of the American Chemical Society
|November 7, 2002
PubMed
Summary
This summary is machine-generated.

New solid-state NMR methods using separate-local-field spectroscopy characterize quadrupolar nuclei. These techniques correlate spectral patterns to assign resonances and study dynamics in solids.

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Area of Science:

  • Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
  • Materials Science
  • Physical Chemistry

Background:

  • Characterizing resonances in solid-state NMR spectroscopy of half-integer quadrupolar nuclei presents challenges.
  • Existing methods may not fully resolve inequivalent sites or dynamics in complex solid materials.

Purpose of the Study:

  • To explore novel approaches for characterizing resonances in solid-state NMR of half-integer quadrupolar nuclei.
  • To develop advanced NMR techniques for assigning resonances to specific structural environments and investigating molecular dynamics.

Main Methods:

  • Acquisition of heteronuclear separate-local-field spectra on rotating solids.
  • Development of two-dimensional (2D) experiments correlating second-order quadrupolar MAS powder patterns with dipolar MAS sideband patterns.
  • Extension to three-dimensional (3D) NMR sequences for separating inequivalent chemical sites along an isotropic dimension.

Main Results:

  • Demonstrated the correlation of quadrupolar MAS powder patterns with dipolar MAS sideband patterns for specific chemical sites.
  • Successfully separated inequivalent resonances using 3D NMR sequences based on anisotropic correlation spectra.
  • Illustrated the application of these methods with 1H-23Na recoupling experiments on mononucleotides.

Conclusions:

  • Extended separate-local-field NMR approaches to quadrupolar nuclei, facilitating resonance assignment to specific structural environments.
  • Provided new tools for the investigation of dynamics in solid-state materials.
  • Validated the utility of these 2D and 3D NMR experiments through practical applications.