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Amines to Sulfonamides: The Hinsberg Test

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The Hinsberg test is a method to identify primary, secondary and tertiary amines, named after its pioneer, Oscar Hinsberg. Here, amines are treated with benzenesulfonyl chloride, also known as the Hinsberg reagent, in the presence of an excess of aqueous base, followed by acidification. Based on the nature of the amines, different changes are observed.
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The word “nucleophile” has a Greek root and translates to nucleus-loving. Nucleophiles are either negatively charged or neutral species with a pair of electrons in a high-energy occupied molecular orbital (HOMO). As these species tend to donate electron pairs, nucleophiles are considered Lewis bases as well. Negatively charged species, like OH−, Cl−, or HS−, with one or several pairs of electrons, are typically nucleophiles. Similarly, neutral species such as...

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Systematic Testing of the Maximum Hardness and Minimum Electrophilicity Principles.

Abdul Rahman Al Nabulsi¹, Farnaz Heidar-Zadeh², PaulPaul W Ayers¹

¹Department of Chemistry and Chemical Biology, McMaster University, Hamilton L8S 4M1, Ontario, Canada.

The Journal of Physical Chemistry. A

|April 10, 2026

Summary

The principles of maximum hardness and minimum electrophilicity offer reliable chemical reaction predictions, particularly for exothermic reactions. Their accuracy improves when reactions violating the hard/soft acid/base rule are excluded.

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Area of Science:

Quantum Chemistry
Theoretical Chemistry

Background:

The principles of maximum hardness and minimum electrophilicity are theoretical concepts used to predict chemical reaction outcomes.
Assessing their reliability is crucial for advancing predictive chemical modeling.

Purpose of the Study:

To evaluate the predictive accuracy of the maximum hardness principle and minimum electrophilicity principle.
To investigate the influence of reaction exothermicity and adherence to the hard/soft acid/base (HSAB) rule on these principles' reliability.

Main Methods:

Computational study of double-exchange reactions involving 496 heteronuclear diatomic molecules.
Analysis of reaction energies and chemical descriptors to test the principles against observed outcomes.
Systematic removal of reactions violating the HSAB rule to assess its impact.

Main Results:

Both principles demonstrate reasonable robustness, especially for exothermic reactions, but are not universally perfect predictors.
Excluding reactions that violate the HSAB rule significantly enhances the reliability of the maximum hardness principle.
When near-thermoneutral reactions are removed, both principles show approximately 80% reliability.
For strongly favored reactions adhering to the HSAB rule, maximum hardness principle accuracy approaches 90%.

Conclusions:

The maximum hardness and minimum electrophilicity principles serve as valuable rules-of-thumb in chemical reactivity predictions.
A strong correlation exists between the maximum hardness principle and the HSAB rule, with the latter improving the former's predictive power.
These principles offer a practical framework for predicting chemical reaction products, especially under specific conditions like strong energetic favorability and HSAB compliance.