SolomonsLKChapter10

SolomonsLKChapter10 - Chapter 10 Radical Reactions " What...

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Chapter 10 Radical Reactions
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t Often called free radicals t Formed by homolytic bond cleavage t Radicals are highly reactive, short-lived species l Half-headed arrows are used to show movement of single electrons Radicals are intermediates with an unpaired electron H . Cl . Hydrogen radical Chlorine radical What are radicals? Methyl radical
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t Usually begins with homolysis of a relatively weak bond such as O-O or X-X t Initiated by addition of energy in the form of heat or light Production of radicals
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t Radicals seek to react in ways that lead to pairing of their unpaired electron and completing a full octet. t Reaction of a radical with any species that does not have an unpaired electron will produce another radical l Hydrogen abstraction is one way a halogen radical can react to pair its unshared electron Reactions of radicals
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Electronic structure of methyl radical
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Atoms have higher energy (are less stable) than the molecules they can form Breaking covalent bonds requires energy ( i.e., it is endothermic) Bond Dissociation Energies
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Consider the possible reaction of H 2 with Cl 2 Example of using Bond Dissociation Energies Reaction is exothermic, more energy is released in forming the 2 H-Cl bonds of product than is required to break the H-H and Cl-Cl bonds of reactants
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Table of bond dissociation energies in text, p. 430
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Relative stability of organic radicals Compare the Bond Dissociation Energies for the primary and secondary hydrogens in propane Since less energy is needed to form the isopropyl radical (from same starting material), the isopropyl radical must be more stable. Diff = 10 kJ/mol
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Using the same table, the tert -butyl radical is more stable than the isobutyl radical Relative Stability of organic radicals Diff = 22 kJ/mol
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same trend as for carbocations l The more substituted radical is the more stable. l
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This note was uploaded on 12/22/2011 for the course CHEMISTRY 2210 taught by Professor Keller during the Spring '11 term at FIU.

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SolomonsLKChapter10 - Chapter 10 Radical Reactions " What...

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