lec 12 - Organic Lecture Series CH 310/318 M LECTURE 12...

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Organic Lecture Series 1 CH 310/318 M LECTURE 12 Textbook Assignment: Chap. 7- Alkynes Today’s Topics: Oxidation Oxidation -Reduction Additions Reduction Additions -Alkenes Alkenes Notice & Announcements: (HW 4 Posted) Organic Lecture Series 2 Reactions Reactions of Alkenes of Alkenes Chapter 6 Chapter 6
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Organic Lecture Series 3 • Treatment of an alkene with Br 2 or Cl 2 in water forms a halohydrin. • Halohydrin: Halohydrin: A compound containing -OH and -X on adjacent carbons. CH 3 CH=CH 2 Cl 2 H 2 OC H 3 CH-CH 2 HO HCl 1-Chloro-2-propanol (a chlorohydrin) Propene + + + Additions of HOCl and HOBr From last lecture: Organic Lecture Series 4 – Reaction is both regioselective (OH adds to the more substituted carbon) and anti stereoselective. – Both selectivities are illustrated by the addition of HOBr to 1-methylcyclopentene. – To account for the regioselectivity and the anti stereoselectivity, chemists propose a three-step mechanism. 2-Bromo-1-methylcyclopentanol ( a racemic mixture ) Br 2 /H 2 O OH 1-Methylcyclopentene + HBr + H H Additions of HOCl and HOBr Additions of HOCl and HOBr
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Organic Lecture Series 5 Step 1: Formation of a bridged halonium ion intermediate CC Br R H H H R H H H R H H H -Br - bridged bromonium ion minor contributing structure : : : : : : : : : Additions of HOCl and HOBr Additions of HOCl and HOBr Organic Lecture Series 6 Step 2: Attack of H 2 O on the more substituted carbon opens the three-membered ring. O H H H R O H HH H + R H H H : : : : : Additions of HOCl and HOBr Additions of HOCl and HOBr
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Organic Lecture Series 7 Step 3: Proton transfer to H 2 O completes the reaction H 3 O + + CC Br O H H H R •• H H + OH H Br O H H H R H Additions of HOCl and HOBr Additions of HOCl and HOBr R C O R C OR' O R C H O R C R' R C O H Carboxylic Acids & Esters Ketones Aldehydes Alcohols R C H H Hydrocarbon (lowest oxidation) Oxidation Reduction
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Organic Lecture Series 9 • Oxymercuration followed by reduction results in hydration of a carbon-carbon double bond. • The addition follows Markovnikov’s rule OH HgOAc NaB H 4 H CH 3 COH O Hg 2-Pentanol + Acetic acid + Hg(OAc) 2 H 2 O HgOAc 3 O Acetic acid An organomercury compound Mercury(II) acetate 1-Pentene + ++ Oxymercuration/Reduction Oxymercuration/Reduction Organic Lecture Series 10 An important feature of oxymercuration/reduction is that it occurs without rearrangement.
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lec 12 - Organic Lecture Series CH 310/318 M LECTURE 12...

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