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Related Concept Videos

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...
¹H NMR of Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
¹H NMR Signal Integration: Overview00:58

¹H NMR Signal Integration: Overview

The intensity of a signal, which can be represented by the area under the peak, depends on the number of protons contributing to that signal. The area under each peak is shown as a vertical line called an integral, with the integral value listed under it, as seen in the proton NMR spectrum of benzyl acetate. Each integral value is divided by the smallest integral value to obtain the ratio of the number of protons producing each signal. The ratio reveals the relative number of protons and not...
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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Relaxation-encoded NMR experiments for mixture analysis: REST and beer.

G Dal Poggetto1, L Castañar1, R W Adams1

  • 1School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. mathias.nilsson@manchester.ac.uk.

Chemical Communications (Cambridge, England)
|June 2, 2017
PubMed
Summary

Researchers developed new nuclear magnetic resonance (NMR) experiments called Relaxation-Encoded Selective TOCSY (REST) to analyze complex mixtures. These methods enable the isolation of individual component spectra from mixtures by leveraging spin relaxation times.

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Area of Science:

  • Analytical Chemistry
  • Spectroscopy
  • Biophysics

Background:

  • Analyzing complex mixtures using traditional NMR spectroscopy can be challenging due to spectral overlap.
  • Component-resolved NMR spectroscopy is crucial for detailed analysis of individual molecules within mixtures.
  • Existing methods often require extensive experimental optimization or specific sample properties.

Purpose of the Study:

  • To introduce a novel family of NMR experiments, Relaxation-Encoded Selective TOCSY (REST), for enhanced mixture analysis.
  • To demonstrate the capability of REST experiments in extracting component-specific subspectra.
  • To utilize spin relaxation properties for differentiating and isolating spectral information from individual mixture components.

Main Methods:

  • Development of a new NMR pulse sequence incorporating isotropic mixing.
  • Application of relaxation-encoded principles to selectively label entire spin systems.
  • Acquisition and processing of NMR data from various mixture samples.
  • Analysis of extracted component subspectra to confirm their origin and purity.

Main Results:

  • Successful extraction of distinct component subspectra from complex mixtures.
  • Demonstration that relaxation times (T1, T2) of individual spins can be used to encode spectral information.
  • Validation of the REST methodology across different types of mixtures.
  • Preservation of complete spin system information within the extracted subspectra.

Conclusions:

  • The Relaxation-Encoded Selective TOCSY (REST) experiments provide a powerful new tool for NMR mixture analysis.
  • REST enables the simplification of complex spectra by isolating individual component subspectra.
  • This approach offers a versatile strategy for characterizing components in mixtures without prior knowledge of their properties.