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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
2D NMR: Overview of Heteronuclear Correlation Techniques01:18

2D NMR: Overview of Heteronuclear Correlation Techniques

Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other axis.
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
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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NMR 15N Relaxation Experiments for the Investigation of Picosecond to Nanoseconds Structural Dynamics of Proteins
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Long-range proton-carbon coupling constants: NMR methods and applications.

Teodor Parella1, Juan Félix Espinosa

  • 1Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. teodor.parella@uab.cat

Progress in Nuclear Magnetic Resonance Spectroscopy
|August 22, 2013
PubMed
Summary

This review covers new nuclear magnetic resonance (NMR) methods for measuring long-range proton-carbon coupling constants in small molecules. It details various NMR experiments, their accuracy, and applications in structural analysis.

Keywords:
E.COSYHMBCHSQC-TOCSYHSQMBCIPAPJ-resolvedLong-range proton–carbon coupling constants

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NMR 15N Relaxation Experiments for the Investigation of Picosecond to Nanoseconds Structural Dynamics of Proteins
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Area of Science:

  • Organic Chemistry
  • Analytical Chemistry
  • Spectroscopy

Background:

  • Accurate measurement of heteronuclear long-range proton-carbon coupling constants ((n)JCH; n>1) is crucial for molecular structure determination.
  • Traditional methods may have limitations in sensitivity, applicability, or accuracy for certain molecular systems.

Purpose of the Study:

  • To provide a comprehensive review of novel nuclear magnetic resonance (NMR) techniques for measuring long-range proton-carbon coupling constants ((n)JCH; n>1) in small molecules.
  • To classify and evaluate these NMR methods based on pulse scheme and cross-peak characteristics.

Main Methods:

  • Classification of NMR experiments based on pulse sequence design and the nature of observed cross-peaks.
  • Detailed discussion and exemplification of the simplicity, general applicability, and accuracy of each NMR method.
  • Exploration of techniques for sign determination and measurement of small coupling constants.

Main Results:

  • A systematic overview of advanced NMR methodologies for quantifying (n)JCH couplings.
  • Evaluation of the strengths and limitations of different NMR experiments, including those for protonated and non-protonated carbons.
  • Highlighting the complementarity of various NMR approaches for comprehensive structural analysis.

Conclusions:

  • Novel NMR methods offer enhanced capabilities for measuring heteronuclear long-range couplings.
  • These techniques are valuable tools for detailed structural and conformational analysis of diverse small molecules.
  • The review provides a practical guide to selecting appropriate NMR experiments for specific analytical challenges.