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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...
Carbon-13 (¹³C) NMR: Overview01:10

Carbon-13 (¹³C) NMR: Overview

Carbon-13 is a naturally occurring NMR-active isotope of carbon with a low natural abundance of 1.1%. In contrast, carbon-12 is the most abundant isotope of carbon with zero nuclear spin. Therefore, it is NMR inactive. The gyromagnetic ratio of carbon-13 is smaller than that of protons. As a result, carbon-13 resonance is about 6000 times weaker than proton resonance. For a given magnetic field strength, the resonance frequency of carbon-13 is about one-fourth of the resonance frequency for...
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: 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...
Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei in a...
¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons00:58

¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons

Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...

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Updated: May 18, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

Chemical shift tensor determination using magnetically oriented microcrystal array (MOMA): 13C solid-state CP NMR

R Kusumi1, F Kimura, G Song

  • 1Division of Forest and Biomaterials Science, Kyoto University, Kyoto 606-8502, Japan.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|September 15, 2012
PubMed
Summary
This summary is machine-generated.

Researchers determined chemical shift tensors for L-alanine crystals using a magnetically oriented microcrystal array (MOMA). This technique accurately analyzes microcrystalline powders, aligning them like a single crystal for detailed analysis.

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High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

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Area of Science:

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

Background:

  • Determining precise chemical shift tensors is crucial for understanding molecular structure and dynamics in solid-state materials.
  • Traditional methods often require large, high-quality single crystals, which are not always available.
  • Microcrystalline powders are abundant but challenging to analyze using single-crystal techniques.

Purpose of the Study:

  • To develop and validate a novel method for determining chemical shift tensors from microcrystalline powder samples.
  • To apply this method to L-alanine, a common amino acid, and compare results with existing literature data.
  • To demonstrate the utility of magnetically oriented microcrystal arrays (MOMA) for solid-state NMR analysis.

Main Methods:

  • Preparation of a magnetically oriented microcrystal array (MOMA) from L-alanine microcrystalline powder.
  • Alignment of microcrystals in three dimensions within a matrix resin to create a single-crystal-like composite.
  • Application of the single-crystal rotation method to the MOMA to extract chemical shift tensor parameters.
  • Analysis of carboxyl and methyl carbon resonances in L-alanine.

Main Results:

  • Successfully determined the chemical shift tensors for the carboxyl and methyl carbons of L-alanine.
  • The obtained principal values and axes of the chemical shift tensors showed excellent agreement with literature values for L-alanine single crystals.
  • Validation of the MOMA technique for accurate tensor determination.

Conclusions:

  • The magnetically oriented microcrystal array (MOMA) technique is a powerful and effective tool for determining chemical shift tensors from microcrystalline powder samples.
  • This method overcomes limitations associated with obtaining large single crystals for solid-state NMR studies.
  • The MOMA approach offers a viable alternative for structural and dynamic analysis of various crystalline materials.