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Related Experiment Video

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Comparative Study of Simulation of Temperature Rise in Ring Main Unit

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Published on: July 5, 2024

Obtaining relative induced ring currents quantitatively from NICS.

Amnon Stanger¹

¹Schulich faculty of Chemistry and The Lise-Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel. stanger@tx.technion.ac.il

The Journal of Organic Chemistry

|March 4, 2010

Summary

A new model quantifies the sigma-only effect on nucleus-independent chemical shift (NICS). Subtracting this from conjugated systems isolates pi-system NICS, revealing ring current strengths and accuracy.

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Area of Science:

Quantum Chemistry
Computational Chemistry
Organic Chemistry

Background:

Nucleus-independent chemical shift (NICS) is a key metric for aromaticity.
Existing methods often struggle to isolate the contributions of sigma and pi electrons to NICS.
Understanding these contributions is crucial for predicting and explaining chemical reactivity and stability.

Purpose of the Study:

Introduce a novel computational model to isolate the sigma-electron contribution to NICS.
Develop a method to quantitatively assess the NICS originating solely from pi-electron systems.
Provide a tool to accurately measure the relative strengths of diatropic and paratropic ring currents.

Main Methods:

A "sigma-only" model was developed to calculate NICS contributions from sigma electrons.
The sigma-only NICS values were subtracted from the total NICS values of conjugated systems.
This subtraction isolates the NICS originating purely from pi-electron delocalization.

Main Results:

The model successfully isolates the pi-system's contribution to NICS.
Quantitative measures of diatropic and paratropic ring currents were obtained for various systems.
The model incorporates an intrinsic measure of its own accuracy.

Conclusions:

The proposed model provides a reliable method for dissecting NICS into sigma and pi contributions.
This approach offers a more accurate understanding of aromaticity and ring currents in chemical systems.
The method's scope and limitations have been discussed, validating its applicability.