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NMR Spectroscopy of Benzene Derivatives

NMR Spectroscopy of Benzene Derivatives

Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling...

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Related Experiment Video

Updated: May 21, 2025

Extraction and Analysis of Taiwanese Green Propolis

Extraction and Analysis of Taiwanese Green Propolis

Published on: January 7, 2019

Compositional Differences Between Brazilian and Chinese Propolis.

Sierra R Parkinson¹, Francelia J Eckembrecher², Lazaro Antonio Toledo Machin³

¹From the University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina, USA.

Dermatitis : Contact, Atopic, Occupational, Drug

|March 20, 2025

Summary

This summary is machine-generated.

Recent increases in propolis allergy reactions are linked to significant compositional differences between Brazilian and Chinese propolis. These variations in chemical makeup likely explain the rise in positive patch tests.

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Published on: March 31, 2021

Area of Science:

Analytical Chemistry
Natural Products Chemistry
Dermatology

Background:

Increased prevalence of positive patch test reactions to propolis.
Variability in reaction rates depending on propolis manufacturer.

Purpose of the Study:

To compare the chemical compositions of Brazilian and Chinese propolis.
To investigate potential reasons for increased propolis allergy prevalence.

Main Methods:

Electrospray ionization mass spectrometry (ESI-MS) for sample analysis.
Identification of compounds using mzCloud, ChemSpider, and MassList databases.
Data processing with Compound Discoverer software to identify top compounds.

Main Results:

Very low compositional overlap between Brazilian and Chinese propolis (8-27% similarity).
Distinct sets of major compounds identified in each propolis type.
Prenylgermacrene B was the only common compound among the top six in both samples.

Conclusions:

Significant chemical differences exist between Brazilian and Chinese propolis.
The discontinuation of Chinese propolis (NA71) and replacement with Brazilian propolis (NH400) by a manufacturer may explain increased allergic reactions.
Chemical variability is a critical factor in propolis-related contact dermatitis.