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Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 10, Problem 16a

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.
(a) Two cyclohexane structures with hydrogen atoms highlighted, comparing bond-dissociation energy.

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1
Understand the concept of bond-dissociation energy: Bond-dissociation energy is the energy required to break a bond in a molecule, resulting in the formation of radicals. The stability of the resulting radicals plays a crucial role in determining the bond-dissociation energy.
Identify the types of radicals formed: When a bond is broken, two radicals are formed. The stability of these radicals can be influenced by factors such as resonance, hyperconjugation, and the presence of electron-withdrawing or electron-donating groups.
Evaluate the stability of the radicals: More stable radicals are typically formed from bonds with lower bond-dissociation energies. Stability can be assessed by considering the number of resonance structures, the degree of hyperconjugation, and the presence of stabilizing groups.
Compare the radicals from each bond pair: For each pair of bonds, compare the stability of the radicals formed. The bond that forms less stable radicals will generally have a higher bond-dissociation energy.
Predict the bond with higher bond-dissociation energy: Based on the stability analysis, predict which bond in each pair will have the higher bond-dissociation energy. The bond forming less stable radicals will require more energy to dissociate.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bond-Dissociation Energy

Bond-dissociation energy is the energy required to break a bond in a molecule, resulting in the formation of radicals. It is a measure of bond strength; higher energy indicates a stronger bond. Understanding this concept helps predict which bonds are more stable and less likely to dissociate.
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How to calculate enthalpy using bond dissociation energies.

Radical Stability

Radical stability refers to the ability of a radical to exist without undergoing further reactions. Stability is influenced by factors such as resonance, hyperconjugation, and the electronegativity of atoms involved. More stable radicals are typically formed from weaker bonds, which have lower bond-dissociation energies.
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Resonance

Resonance is the delocalization of electrons across adjacent atoms, which can stabilize radicals by spreading out the electron density. Molecules with resonance structures often have lower bond-dissociation energies because the resulting radicals are more stable. Recognizing resonance can help predict radical stability and bond strength.
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