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Related Concept Videos

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...
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...
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...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
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...

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Related Experiment Video

Updated: May 30, 2026

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode
09:19

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode

Published on: June 4, 2021

Statistical filtering for NMR based structure generation.

Jochen Junker1

  • 1Fundação Oswaldo Cruz - CDTS, Rio de Janeiro - RJ, Brazil. junker@cdts.fiocruz.br.

Journal of Cheminformatics
|August 13, 2011
PubMed
Summary

This study introduces a statistical filter to improve natural product structure elucidation using NMR data. The filter effectively reduces incorrect solutions generated by computer programs, ensuring the correct structure remains.

Area of Science:

  • Chemistry
  • Spectroscopy
  • Computational Chemistry

Background:

  • Natural product structure elucidation relies on 2D NMR (COSY, HSQC, HMBC).
  • Assigning structures of complex molecules like condensed heterocycles is challenging.
  • Computer programs like COCON aid structure elucidation but can generate numerous possibilities.

Purpose of the Study:

  • To present a statistical filter for reducing the number of potential solutions in structure elucidation.
  • To enhance the accuracy and efficiency of computer-assisted natural product assignment.
  • To refine computational methods for analyzing NMR data.

Main Methods:

  • Utilized a statistical filter incorporating 3D conformation generation via a simple molecular dynamics (MD) approach (smi23d).

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  • Eliminated molecules where constitutional restraints could not be generated.
  • Integrated automatic removal of molecules lacking MD parameter sets into WEBCOCON.

    • Main Results:

    • The statistical filter successfully reduced the number of incorrect solutions generated by structure elucidation software.
    • Analysis of removed structural elements against Beilstein confirmed filter efficacy.
    • The correct molecular constitution was never removed from the result set by the filter.

    Conclusions:

    • The developed statistical filter is a valuable tool for improving the accuracy of NMR-based structure elucidation.
    • This method enhances computational approaches by efficiently filtering out improbable molecular structures.
    • The filter's integration into WEBCOCON offers a more robust solution for complex natural product analysis.