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Related Concept Videos

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT)01:15

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT)

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) is an advanced Nuclear Magnetic Resonance (NMR) technique specifically designed to detect and enhance the signals of low-abundance nuclei, such as carbon-13 and nitrogen-15, in small molecules. The fundamental principle behind INEPT is the transfer of polarization from a more abundant and highly polarizable nucleus, typically hydrogen-1, to the low-abundance nucleus of interest. This process effectively boosts the NMR signal of the...
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: 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...
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...
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...
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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Quantitative (13)C NMR spectroscopy using refocused constant-time INEPT, Q-INEPT-CT.

A V Mäkelä1, I Kilpeläinen, S Heikkinen

  • 1Laboratory of Organic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 University of Helsinki, Finland. valtteri.makela@iki.fi

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|March 19, 2010
PubMed
Summary

Quantitative Carbon-13 NMR (13C NMR) is often slow. A new Q-INEPT-CT pulse sequence improves sensitivity and speed for quantitative 13C NMR analysis of mixtures.

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Area of Science:

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry

Background:

  • Quantitative NMR spectroscopy is crucial for mixture analysis.
  • Proton NMR (1H NMR) is common, but Carbon-13 NMR (13C NMR) offers better signal dispersion.
  • Traditional 13C NMR is time-consuming due to low natural abundance and long relaxation times.

Purpose of the Study:

  • To develop a faster and more sensitive method for quantitative 13C NMR.
  • To overcome limitations of traditional quantitative 13C NMR techniques.
  • To enable rapid analysis of low-concentration samples.

Main Methods:

  • Development of a novel pulse sequence: constant-time Insensitive Nucleate Exchange (INEPT), termed Q-INEPT-CT.
  • Utilizing polarization transfer experiments for enhanced signal intensity.
  • Implementing constant-time sequence for easier relaxation correction.

Main Results:

  • The Q-INEPT-CT sequence yields quantitative carbon spectra.
  • Achieves better sensitivity and/or reduced acquisition time compared to traditional methods.
  • Minimizes signal loss due to relaxation effects through constant sequence length.

Conclusions:

  • Q-INEPT-CT is a valuable tool for rapid quantitative 13C NMR.
  • Enables efficient analysis of complex mixtures and low-concentration samples.
  • Improves upon existing techniques for quantitative carbon NMR spectroscopy.