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On the origin of the steric effect
Balazs Pinter1, Tim Fievez, F Matthias Bickelhaupt
1Eenheid Algemene Chemie, QCMM VUB-UGent Alliance Research Group, Vrije Universiteit Brussel, Pleinlaan 2, Brussel, Belgium. pbalazs@vub.ac.be
Physical Chemistry Chemical Physics : PCCP
|June 16, 2012
Summary
This study quantifies steric effects in chemical reactions, separating steric strain and shielding. It reveals how these factors, originating from Pauli repulsion, influence reactivity and reaction rates.
Area of Science:
- Computational Chemistry
- Organic Chemistry
- Physical Chemistry
Background:
- Steric effects significantly influence chemical reaction rates and mechanisms.
- Existing models for steric effects lack a clear, quantitative distinction between strain and shielding.
- Understanding these effects is crucial for predicting and controlling chemical reactivity.
Purpose of the Study:
- To develop a quantitative framework for analyzing the steric effect of aliphatic groups from first principles.
- To differentiate and interpret the contributions of steric strain and steric shielding to reactivity.
- To establish a correlation between computational findings and established steric parameters.
Main Methods:
- Quantitative analysis of steric effects using first-principles calculations.
- Decomposition of steric effects into strain and shielding components.
- Correlation of calculated steric parameters with Taft's steric parameters.
Main Results:
- A framework was developed to separate steric strain and steric shielding.
- Steric shielding correlates with Taft's parameters, explaining reduced accessibility of reactive centers.
- Steric strain arises from Pauli repulsion, causing substrate deformation and destabilizing the reaction zone.
Conclusions:
- Both steric strain and steric shielding are manifestations of Pauli repulsion between reactants.
- The proposed framework provides a clear interpretation of steric effects in chemical reactions.
- This work offers a deeper understanding of how molecular structure impacts reactivity.
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