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Related Concept Videos

Electrophiles02:28

Electrophiles

13.0K
This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups.
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Regioselective Formation of Enolates01:33

Regioselective Formation of Enolates

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As depicted in the figure below, the unsymmetrical ketones can form two possible enolates:  less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are  more stable. But the energy required to form kinetic enolates is less.
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Diels–Alder vs Retro-Diels–Alder Reaction: Thermodynamic Factors01:31

Diels–Alder vs Retro-Diels–Alder Reaction: Thermodynamic Factors

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The Diels–Alder reaction is thermally reversible, meaning that the reaction reverts to the starting diene and dienophile under suitable temperatures. The forward reaction gives a cyclohexene derivative and is favored at low to medium temperatures. The reverse process, also called retro-Diels–Alder reaction, is a ring-opening process favored at high temperatures.
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Radical Halogenation: Thermodynamics01:34

Radical Halogenation: Thermodynamics

4.6K
The thermodynamic favorability of a reaction is determined by the change in Gibbs free energy (ΔG). ΔG has two components- enthalpy (ΔH) and entropy (ΔS). The entropy component is negligible for alkane halogenation because the number of reactants and product molecules are equal. In this case, the ΔG is governed only by the enthalpy component. The most crucial factor that determines ΔH is the strength of the bonds. ΔH can be determined by comparing the energy...
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Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes
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Thermodynamic electrophilicity.

Ramón Alain Miranda-Quintana1

  • 1Department of Chemical Physics, Faculty of Chemistry, University of Havana, Havana, Cuba and Department of Chemistry & Chemical Biology, McMaster University, Hamilton, Ontario L8S 4M1, Canada.

The Journal of Chemical Physics
|June 10, 2017
PubMed
Summary

This study revisits the electrophilicity index, highlighting issues with standard calculations. A new finite temperature approach resolves inconsistencies and provides a simpler, exact working equation for this key reactivity descriptor.

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Area of Science:

  • Theoretical Chemistry
  • Quantum Chemistry
  • Chemical Reactivity

Background:

  • The electrophilicity index is a crucial descriptor for chemical reactivity.
  • Standard calculation methods based on zero-temperature conceptual density functional theory (DFT) present inconsistencies.
  • Accurate calculation of reactivity indices is vital for predicting chemical behavior.

Purpose of the Study:

  • To re-examine the electrophilicity index and its calculation methods.
  • To address the limitations and inconsistencies of the zero-temperature DFT approach.
  • To propose a more robust and accurate method for determining the electrophilicity index.

Main Methods:

  • Utilizing the finite temperature grand-canonical formalism.
  • Applying conceptual density functional theory (DFT) principles.
  • Deriving working equations for the electrophilicity index.

Main Results:

  • Identified several issues with the standard calculation of the electrophilicity index.
  • Developed a finite temperature formalism to overcome these inconsistencies.
  • Obtained a simple, exact working equation for the electrophilicity index.

Conclusions:

  • The finite temperature grand-canonical formalism offers a superior approach to calculating the electrophilicity index.
  • This method resolves characteristic inconsistencies found in zero-temperature formulations.
  • The derived exact working equation simplifies electrophilicity calculations in terms of electronic structure.