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Related Concept Videos

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Radical Reactivity: Steric Effects

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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The Arrhenius equation relates the activation energy and the rate constant, k, for chemical reactions. In the Arrhenius equation, k = Ae−Ea/RT, R is the ideal gas constant, which has a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is a constant called the frequency factor, which is related to the frequency of collisions and the orientation of the reacting molecules.
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Bond Dissociation Energy and Activation Energy02:13

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Bond energy is the energy required to break a bond homolytically. These values are usually expressed in units of kcal/mol or kJ/mol and are referred to as bond dissociation energies when given for specific bonds or average bond energies when indicated for a given type of bond over many compounds. Firstly, the bond dissociation energy for a single bond is weaker than that of a double bond, which in turn is weaker than that of a triple bond. Secondly, hydrogen forms relatively strong bonds with...
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The activation energy (or free energy of activation), abbreviated as Ea, is the small amount of energy input necessary for all chemical reactions to occur. During chemical reactions, certain chemical bonds break, and new ones form. For example, when a glucose molecule breaks down, bonds between the molecule's carbon atoms break. Since these are energy-storing bonds, they release energy when broken. However, the molecule must be somewhat contorted to get into a state that allows the bonds to...
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Radical Reactivity: Concentration Effects01:20

Radical Reactivity: Concentration Effects

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In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
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Understanding chemical reactivity using the activation strain model.

Pascal Vermeeren1, Stephanie C C van der Lubbe1, Célia Fonseca Guerra1,2

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This study introduces PyFrag 2019 for analyzing chemical reactions using the activation strain model (ASM). It helps predict reactivity and design new reactions by examining energy changes along reaction pathways.

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Area of Science:

  • Computational Chemistry
  • Chemical Reactivity Analysis

Background:

  • Predicting chemical reactivity is crucial for designing novel reactions.
  • Current methods often analyze single stationary points, limiting comprehensive understanding.

Purpose of the Study:

  • To provide a robust computational protocol for analyzing chemical reactions.
  • To implement the activation strain model (ASM) for detailed reactivity insights.

Main Methods:

  • Utilizing PyFrag 2019 software for reaction analysis.
  • Applying the activation strain model (ASM) to study energy changes along reaction coordinates.
  • Optimizing stationary points and calculating potential energy surfaces.

Main Results:

  • The ASM method analyzes the full energy profile, not just stationary points.
  • This approach offers a deeper understanding of reaction mechanisms.
  • The protocol is applicable across organic, inorganic, supramolecular, and biochemical fields.

Conclusions:

  • The PyFrag 2019 protocol enables comprehensive analysis of chemical reactivity.
  • This method facilitates the prediction and rational design of new chemical reactions.
  • The protocol provides a practical guide for researchers within days.