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Related Concept Videos

¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

1.5K
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...
1.5K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.2K
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...
1.2K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.2K
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...
2.2K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

1.0K
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...
1.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.2K
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,...
1.2K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.3K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.3K

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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
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Resolving Entangled JH-H-Coupling Patterns for Steroidal Structure Determinations by NMR Spectroscopy.

Danni Wu1, Kathleen Joyce Carillo1,2,3, Jiun-Jie Shie1

  • 1Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan.

Molecules (Basel, Switzerland)
|May 5, 2021
PubMed
Summary

High-resolution 1H NMR spectroscopy struggles with complex steroid signals. This study presents a novel method to resolve entangled JH-H splitting patterns, improving steroid structure determination.

Keywords:
J scalar coupling constantsfingerprint patternsproton chemical shiftssteroid hormonesstructural determinations

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Area of Science:

  • Analytical Chemistry
  • Organic Chemistry
  • Spectroscopy

Background:

  • High-resolution 1H NMR spectroscopy is crucial for analyzing steroid hormones and synthetic steroids.
  • Signal superposition and JH-H splitting patterns in 1H NMR spectra complicate the analysis of steroid structures and interactions.
  • Current methods are limited in resolving individual 1H chemical shifts and coupling identities.

Purpose of the Study:

  • To develop a novel scheme for resolving entangled JH-H splitting patterns and 1H chemical shifts in steroids.
  • To overcome limitations in elucidating steroidal molecular structures and steroid/ligand interactions at the atomic level.
  • To provide a universally applicable method for steroid analysis using NMR.

Main Methods:

  • Focused on unraveling entangled JH-H splitting patterns in androstanolone and epiandrosterone (compounds 1 and 2).
  • These compounds differ only in hydroxyl and ketone substituents at C3 and C17.
  • Proposed a simple, novel scheme for resolving complex JH-H splitting patterns and 1H chemical shifts.

Main Results:

  • Demonstrated that deduced JH-H values are universal and applicable to various other steroids (e.g., testosterone, prednisolone, estradiol).
  • Observed that 1H chemical shifts can vary significantly between samples.
  • Successfully proposed a scheme for resolving complex NMR splitting patterns.

Conclusions:

  • The developed scheme effectively resolves entangled JH-H splitting patterns in steroids.
  • The deduced JH-H values show broad applicability across different steroid structures.
  • This method enhances the potential for precise steroidal structure determination using NMR spectroscopy.