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Nuclear Magnetic Resonance (NMR): Overview01:07

Nuclear Magnetic Resonance (NMR): Overview

Nuclear magnetic resonance (NMR) is a phenomenon exhibited by certain nuclei that can absorb characteristic radio frequency radiation under certain conditions. NMR has been extensively applied in molecular spectroscopy and medical diagnostic imaging. In both these applications, the molecule or subject under study is placed in a magnetic field and irradiated with radio frequency energy.
NMR spectroscopy generates a spectrum where the characteristic absorption frequencies of the sample are...
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.
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.
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...
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.

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Updated: Jul 21, 2026

Concentration of Metabolites from Low-density Planktonic Communities for Environmental Metabolomics using Nuclear Magnetic Resonance Spectroscopy
11:47

Concentration of Metabolites from Low-density Planktonic Communities for Environmental Metabolomics using Nuclear Magnetic Resonance Spectroscopy

Published on: April 7, 2012

Bases de datos universales de RMN para los polioles contiguos.

Shuhei Higashibayashi1, Werngard Czechtizky, Yoshihisa Kobayashi

  • 1Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.

Journal of the American Chemical Society
|November 20, 2003
PubMed
Resumen

Este estudio introduce bases de datos de RMN para la estereoquímica de polioles, desarrollando métodos que utilizan constantes de acoplamiento de espín como predictores primarios y cambios químicos como confirmaciones secundarias. Los efectos gamma y delta refinan las predicciones para estereoisómeros específicos.

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Concentration of Metabolites from Low-density Planktonic Communities for Environmental Metabolomics using Nuclear Magnetic Resonance Spectroscopy
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Área de la Ciencia:

  • Química orgánica es la química orgánica.
  • La espectroscopia es una técnica de espectroscopia.
  • Química computacional es la química computacional.

Sus antecedentes:

  • Las bases de datos de resonancia magnética nuclear (RMN) son cruciales para el análisis de moléculas orgánicas complejas.
  • Los polioles presentan desafíos estereoquímicos debido a los múltiples grupos hidroxilo.
  • Los métodos predictivos para la estereoquímica de polioles requieren herramientas analíticas robustas.

Objetivo del estudio:

  • Desarrollar y evaluar bases de datos de RMN para el análisis estereoquímico de polioles.
  • Evaluar la utilidad de varios descriptores de perfiles de RMN, incluidos los desplazamientos químicos y las constantes de acoplamiento de espín.
  • Para refinar los modelos predictivos mediante la incorporación de efectos estereoquímicos específicos.

Principales métodos:

  • Construcción de bases de datos de RMN con el uso de 1,2,3-triolos, 1,2,3,4-tetraolos y 1,2,3,4,5-pentaolos.
  • Aplicación de descriptores de perfiles: (13) C-, (1) H- y (1) H-OH desplazamientos químicos y las constantes de acoplamiento de espín de vecindad ((3) J-H, H)).
  • Estudio de caso sobre heptaols para analizar los efectos gamma y delta en las predicciones de desplazamiento químico y evaluar los perfiles (3) J(H, H).

Principales resultados:

  • Las bases de datos de RMN para polioles se establecieron utilizando múltiples tipos de descriptores.
  • Los efectos gamma y delta fueron identificados como significativos para refinar las predicciones de desplazamiento químico en subgrupos específicos de estereoisómeros.
  • Se desarrollaron dos métodos para el análisis estereoquímico utilizando perfiles contiguos (3) J, H, H (tres y dos constantes).
  • Se encontró que el análisis utilizando perfiles (3) J ((H, H) era operacionalmente más simple que usar perfiles de desplazamiento químico.

Conclusiones:

  • (3) Los perfiles J, H, H se recomiendan como la herramienta principal para predecir la estereoquímica de poliol debido a su simplicidad y eficacia.
  • (13) Los perfiles de desplazamiento químico C y (1) H sirven como valiosas herramientas secundarias para confirmar la predicción de la estereoquímica.
  • El estudio proporciona un enfoque refinado para el análisis estereoquímico de poliol, mejorando la precisión y la eficiencia.