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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
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: Pople Notation01:09

¹H NMR: Pople Notation

The Pople nomenclature system classifies spin systems based on the difference between their chemical shifts. Coupled spins are denoted by capital letters with subscripts indicating the number of equivalent nuclei. When the coupled nuclei have well-separated chemical shifts, they are assigned letters that are far apart in the alphabet, such as A and X. When the difference in chemical shifts is small, coupled nuclei are named using adjacent letters of the alphabet (AB, MN, or XY).
A proton...
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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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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1H/31P distance determination by solid state NMR in multiple-spin systems.

Maggy Hologne1, Philippe Bertani, Thierry Azaïs

  • 1Institut de Chimie, FRE 2446 CNRS, Université Louis Pasteur, BP 296, 67008 Strasbourg Cedex, France.

Solid State Nuclear Magnetic Resonance
|May 19, 2005
PubMed
Summary
This summary is machine-generated.

Comparing dipolar recoupling techniques, REDOR and Cross-Polarization Magic Angle Spinning (CPMAS), reveals distinct behaviors in multiple-spin systems. REDOR preserves interactions, while CPMAS truncates them due to Hamiltonian non-commutativity.

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Area of Science:

  • Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
  • Quantum dynamics

Background:

  • Dipolar recoupling techniques are crucial for structure determination in solid-state NMR.
  • Understanding spin dynamics in multi-spin systems is essential for interpreting NMR data.
  • REDOR and CPMAS are commonly used dipolar recoupling methods with differing theoretical underpinnings.

Purpose of the Study:

  • To compare the behavior of Rotational Echo DOuble Resonance (REDOR) and Cross-Polarization Magic Angle Spinning (CPMAS) in a coupled multiple-spin system.
  • To elucidate the fundamental differences in spin dynamics governed by these two techniques.

Main Methods:

  • Experimental comparison of REDOR and CPMAS on a model system.
  • Theoretical analysis of the dipolar Hamiltonian for both techniques.
  • Spin dynamics calculations to validate experimental observations.

Main Results:

  • REDOR preserves all dipolar interactions (S-I(k)) as they commute, leading to observable splittings with each added spin.
  • CPMAS truncates weak coupling terms from neighboring spins (I(k)) due to non-commutativity of flip-flop terms with the dominant spin pair interaction.
  • Spin dynamics calculations accurately reproduced experimental data for a cubane-shaped cluster.

Conclusions:

  • REDOR and CPMAS exhibit fundamentally different behaviors in coupled multiple-spin systems.
  • The observed differences are attributed to the commutativity properties of the dipolar Hamiltonian terms under each technique.
  • These findings provide a deeper understanding of the strengths and limitations of REDOR and CPMAS for structural studies.