Lecture 2 - Cl-118 Br 2 I 2 113-71 42 h υ or Δ...

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1 Reading for Wednesday ± Sections 15.11-15.14 Mon. 6:00-7:30 pm MAL 3092 Tues. 2:30-4:00 PM MAL 2007 Wed. 5:00-6:30 PM MAL 2001 Thurs. 9:30-10:50 AM MAL 1003 Sat. 11:00 AM-1:00 PM MAL 2007 Sessions begin TODAY! CHEM 626 PLUS Sessions Chapter 15 Radical Reactions Halogenation of Alkanes (15.3) Radical substitution reaction R-H + X 2 R-X + H-X X 2 = Cl 2 or Br 2 h υ or Δ Evidence for Radical Chain Mechanism rather than Ionic Mechanism (15.4) Light, heat, or added peroxide (ROOR) is necessary for the reaction O 2 inhibits the reaction No rearrangements are observed Unlike carbocations, radicals do not rearrange Energetics of Ethane Chlorination
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2 Comparison with other halogens CH 3 CH 3 + X 2 CH 3 CH 2 -X + H-X X 2 Δ H° (kJ/mol) Prop. 1 Prop. 2 Overall F 2 -159 -289 -448
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Unformatted text preview: Cl 2-21-97-118 Br 2 +42-93-51 I 2 +113-71 +42 h υ or Δ Chlorination vs. Bromination (15.6) • Chlorination is faster than bromination • Chlorination is less selective than bromination • In fact, bromination often leads to a single product. Chlorination of Propane: First Propagation Step is Exothermic less stable 1º radical more stable 2º radical Bromination of Propane: First Propagation Step is Endothermic less stable 1º radical more stable 2º radical Halogenation in Organic Synthesis (15.7) • Bromination generally more useful than chlorination, due to greater selectivity • Chlorination is useful in cases where only one kind of H is present....
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Lecture 2 - Cl-118 Br 2 I 2 113-71 42 h υ or Δ...

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