Organic chem

Organic chem - Last Lecture: FINISHED CHAPTER 10!...

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Last Lecture: FINISHED CHAPTER 10! Substitution reactions of epoxides (10.8) Arene oxides (10.9) Thiols, Sulfides and Sulfonium Salts (10.11) Organometallic compounds (10.12) Coupling Reactions (10.13)
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Chapter 11 Reactions of alkanes. Radicals.
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Alkanes are unreactive compounds (11.1) Alkanes are saturated hydrocarbons (contain only bonds – “C n H 2n+2 ” for acyclics). Alkanes undergo combustion (reaction with O 2 to give CO 2 and H 2 O) and radical type reactions. Chlorination and Bromination (11.2 - 11.4) Reactions with Cl 2 and Br 2 take place at high temperature or with h . F 2 and I 2 are not useful; F 2 reacts violently and I 2 is too unreactive. Homolytic bond cleavage: Cl Cl or h ν 2 Cl Br Br or h ν 2 Br
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Alkanes are unreactive compounds because they have only strong σ bonds and atoms with no partial charges However, alkanes do react with Cl 2 and Br 2
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Reactions of Alkanes - Radicals (9.1 - 9.4) General mechanism (radical chain reaction): Cl Cl or h ν 2 Cl Cl H CH 3 HCl CH 3 CH 3 Cl Cl CH 3 Cl Cl initiation propagation Cl Cl Cl 2 CH 3 CH 3 CH 3 CH 3 Cl CH 3 CH 3 Cl termination major product
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Consider the relative stabilities of alkyl radicals (11.3) Cl H R HCl R Recall one of the propagation steps in free radical halogenation: p 485
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Reactions of Alkanes - Radicals (11.4) Product Distribution: + Cl 2 six 1° H's four 2° H's + Br 2 h ν EXPECTED STATISTICAL YIELD: 60 % 1-halo 40 % 2-halo h ν Cl Cl 29 % 71 % Br Br 2 % 98 %
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Reactions of Alkanes - Radicals (11.4,11.5) Both probability and reactivity must be taken into account. PROBABILITY – HOW MANY IDENTICAL HYDROGENS? REACTIVITY
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This note was uploaded on 10/11/2011 for the course CHEM 2261 taught by Professor Crowe during the Fall '08 term at LSU.

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Organic chem - Last Lecture: FINISHED CHAPTER 10!...

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