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Why and When Is Electrophilicity Minimized? New Theorems and Guiding Rules†
László von Szentpály1, Savaş Kaya2, Nihat Karakuş3
1Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
The Journal of Physical Chemistry. A
|December 10, 2020
Summary
The minimum electrophilicity principle (MEP) generally holds for chemical reactions, but failures occur when product electron affinity increases. This study clarifies MEP
Area of Science:
- Theoretical Chemistry
- Quantum Chemistry
- Chemical Reactivity Theory
Background:
- The minimum electrophilicity principle (MEP) suggests reaction products have lower total electrophilicity than reactants.
- Electrophilicity indices (ω1, ω2) are crucial for predicting reaction outcomes.
- Understanding the conditions and limitations of MEP is vital for chemical reactivity predictions.
Purpose of the Study:
- To investigate the physical basis, validity, and limitations of the minimum electrophilicity principle (MEP).
- To provide an improved understanding of conditions for minimizing electrophilicity indices.
- To compare the performance of two electrophilicity indices (ω1 and ω2) across diverse chemical systems.
Main Methods:
- Calculation of electrophilicity indices (ω1, ω2) using ionization energies (I) and electron affinities (A) from ground-state (GS) and valence-state (VS) energies.
- Analysis of changes in electrophilicity (Δω1, Δω2) for association reactions (X + Y → XY).
- Comparison of MEP with maximum hardness postulate and assessment of failures in various chemical systems.
Main Results:
- New analytical arguments and theorems support MEP, explaining its success over maximum hardness in many association reactions.
- Failures of MEP are linked to increased product electron affinity, as seen in B2, C2, Si2, and CN.
- Size-driven electrophilicity maximization (Δω > 0) explains MEP failures in fullerenes, metal clusters, and liquid water.
Conclusions:
- MEP is a generally successful guiding rule for chemical reactivity but has identifiable limitations.
- Increased product electron affinity and size effects are key reasons for MEP failures.
- Changes in electrophilicity indices offer insights into chemical system reactivity, but MEP is not a universal theoretical basis.
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