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Related Concept Videos

Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
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2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)01:19

2D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)

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Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
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¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

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Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
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¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

1.3K
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
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¹H NMR Signal Integration: Overview00:58

¹H NMR Signal Integration: Overview

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The intensity of a signal, which can be represented by the area under the peak, depends on the number of protons contributing to that signal. The area under each peak is shown as a vertical line called an integral, with the integral value listed under it, as seen in the proton NMR spectrum of benzyl acetate. Each integral value is divided by the smallest integral value to obtain the ratio of the number of protons producing each signal. The ratio reveals the relative number of protons and not...
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NMR and Mass Spectroscopy of Carboxylic Acids01:30

NMR and Mass Spectroscopy of Carboxylic Acids

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In ¹H NMR spectroscopy, acidic protons (–COOH) of carboxylic acids are highly deshielded and absorb far downfield, at around 9–12 ppm. The chemical shift value depends on the concentration and solvent used.
While α protons of carboxylic acids absorb at 2–2.5 ppm, β protons absorb further upfield.
Carboxylic acids are easily identified by dissolving them in deuterium oxide, which results in a rapid exchange of the acidic protons with deuterium. This leads to the...
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Updated: Nov 5, 2025

Color Spot Test As a Presumptive Tool for the Rapid Detection of Synthetic Cathinones
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Quantification of Cathinone Analogues without Reference Standard Using 1H Quantitative NMR.

Yuxin Zhao1,2, Bo Wu1,3, Zhendong Hua2,4

  • 1School of Pharmacy, China Pharmaceutical University.

Analytical Sciences : the International Journal of the Japan Society for Analytical Chemistry
|May 17, 2021
PubMed
Summary

A new 1H quantitative nuclear magnetic resonance (1H qNMR) method accurately quantifies synthetic cathinones, addressing challenges posed by structural variations and lack of reference standards for these novel psychoactive substances.

Keywords:
Quantitative nuclear magnetic resonanceassayquantitationstructure identificationsynthetic cathinones

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Area of Science:

  • Forensic Chemistry
  • Analytical Chemistry
  • Organic Chemistry

Background:

  • Synthetic cathinones are frequently abused novel psychoactive substances (NPS).
  • Rapid structural variations in synthetic cathinones and the lack of reference standards hinder accurate quantification.
  • Developing reliable analytical methods is crucial for identifying and quantifying these substances.

Purpose of the Study:

  • To establish and validate a 1H quantitative nuclear magnetic resonance (1H qNMR) method for the accurate quantification of synthetic cathinones.
  • To utilize a universal signal on the synthetic cathinone core structure for quantitative analysis.
  • To demonstrate the method's applicability to various synthetic cathinone analogues.

Main Methods:

  • Development of a 1H qNMR method using maleic acid as an internal standard.
  • Identification of a shared quantitative peak (methylidyne hydrogen) on the parent synthetic cathinone structure.
  • Optimization of acquisition parameters and comprehensive method validation (specificity, linearity, accuracy, precision, robustness).
  • Application of the validated method to quantify mexedrone and its analogues (3-CEC, 4-Cl-α-PVP, propylone, methcathinone).

Main Results:

  • The established 1H qNMR method demonstrated high accuracy, precision, and robustness.
  • The method successfully quantified mexedrone and several analogues, confirming its versatility.
  • Validation parameters met acceptable criteria, indicating the method's reliability for forensic analysis.

Conclusions:

  • The developed 1H qNMR method provides an accurate, rapid, and versatile solution for the qualitative and quantitative analysis of synthetic cathinones.
  • This approach overcomes limitations associated with reference standard availability for NPS.
  • The method is suitable for addressing forensic challenges related to the identification and quantification of diverse synthetic cathinone compounds.