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Related Concept Videos

NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
NMR Spectrometers: Overview01:20

NMR Spectrometers: Overview

NMR spectrometers consist of a strong magnet, a radiofrequency transmitter, and a detector attached to a computer console for recording spectra of samples containing NMR-active nuclei. In first-generation NMR instruments called continuous-wave spectrometers, the resonance frequencies of the nuclei are determined by frequency-sweep or field-sweep methods. The magnetic field strength is fixed and the rf signal is swept in the former, while the radiofrequency signal is fixed and the magnetic field...
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.
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
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...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...

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Related Experiment Video

Updated: Jul 4, 2026

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale
08:09

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

Published on: April 19, 2021

29Si NMR in solid state with CPMG acquisition under MAS.

J W Wiench1, V S-Y Lin, M Pruski

  • 1U.S. DOE Ames Laboratory, Iowa State University, Ames, IA 50011, USA.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|June 10, 2008
PubMed
Summary

Enhance solid-state NMR sensitivity using Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences for 29Si magnetization detection. This technique improves 1D and 2D NMR spectra of silicates, zeolites, and minerals.

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NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode
09:19

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode

Published on: June 4, 2021

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Last Updated: Jul 4, 2026

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale
08:09

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

Published on: April 19, 2021

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode
09:19

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode

Published on: June 4, 2021

Area of Science:

  • Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
  • Materials Science and Chemistry.

Background:

  • 29Si solid-state NMR is crucial for characterizing silicon-containing materials.
  • Sensitivity limitations can hinder detailed analysis.
  • The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is a known method for signal enhancement.

Purpose of the Study:

  • To demonstrate the effectiveness of CPMG pulse trains for enhancing sensitivity in 29Si solid-state NMR.
  • To showcase the application of CPMG in various 1D and 2D NMR experiments.
  • To analyze the mechanisms and limits of sensitivity enhancement.

Main Methods:

  • Application of rotor-synchronized CPMG pi pulse trains during 29Si magnetization detection.
  • Acquisition of 1D 29Si{X} CPMAS and 2D 29Si{X} HETCOR spectra (X=1H or 27Al).
  • Utilizing fast magic angle spinning (25-40 kHz) for optimal sensitivity gain.
  • Exploration of 29Si-29Si double-quantum techniques for J-coupling measurements.

Main Results:

  • Significant sensitivity enhancement achieved in 29Si solid-state NMR experiments.
  • Successful demonstration across various techniques and material types (mesoporous silicas, zeolites, minerals).
  • Insights into transverse dephasing mechanisms and sensitivity limits provided.
  • CPMG detection shown to be effective for measuring homonuclear J-couplings.

Conclusions:

  • CPMG pulse trains are a powerful tool for boosting 29Si solid-state NMR sensitivity.
  • This approach broadens the applicability of NMR for studying diverse silicon-based materials.
  • The study provides practical guidance on experimental strategies and data processing for maximizing sensitivity.