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CHM247H1 (26)
Chapter 10

Alkyl Halides and Types of Rxns Notes- Lecture and Textbook Chapter 10, 11

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University of Toronto St. George
Cecilia Kutas

CHM247H1 Jasmyn Lee Chapter 10: The Chemistry of the Alkyl Halides 10.1 Names and Properties of Alkyl Halides Organic Halides  R – X and Ar – X I O o Where X = F, Cl, Br, I HO I OH  Halogen compounds in human physiology I O NH2 o Table salt is iodized to prevent goite I thyroxine Cl Cl  Organo Halides from marine organisms o Almost 100 different organic halides have been isolated from edible red seaweed (asparagopsis taxiformis) H CCl3 o DichloroDiphenulTrichloroethane DichloroDiphenylTrichloroethane  DDT is a non-specific pesticide  Kills insects that spread diseases (eg/ malaria, typhys)  Weakly polar, very stable organic molecule  Persists in environment, collects in fatty tissue  Interferes with egg-shell formation of eagles and hawks  Halides are important industrially o Vinyl chloride (CH = CHCl) polymerized to give PVC Alkyl, Vinyl and Aryl Halides  CCl – an alkyl halide, Cl is bonded to an sp carbon 4  F2C=CF 2 a vinyl halide, F is bonded to an sp hybridized carbon (on an isolated double bond)  C6H 5Br – an aryl halide, Br is bonded to an sp hybridized carbon of an aromatic ring Spectroscopy  IR – the C-X bond stretch appears in the fingerprint region (500-800 cm )  hard to identify by IR  1H NMR – H – C – X  2.5δ – 4.0δ ; H is deshielded by the influence of the electronegative X  downfield Preparation of Organic Halides  Review Methods of Preparation 1. Halogenation of Alkenes 2. Hydrohalogenation of Alkenes 3. Allylic and Benzylic Bromination o (Br placed next to C=C) o Double bond left intact (radical mechanism) o N-bromosuccinamide (NBS) – generates a low concentration of Br 2 1 CHM247H1 Jasmyn Lee NBS, h Br CCl 4 H H H Br Br + Br h + HBr 2 NBS h, CC4 4. Conversion of Alcohols to Alkyl Halides o Most frequently used lab method of alkyl halide preparation o 3° alcohol to halide o OH HCl, 0 C Cl ether  3° ROH to 3° RX Mechanism H3C H Cl H 3 H3C H3C H3C + H 3 C+ C OH C OH 2 H3C H3C H3C - Cl (classic S 1 nechanism) H3C N H 3 C Cl H 3 o 1° HalRdes CH OH2 Type Displacement 2 pyridine R CH C2  Need reagents that convert –OH to a better leaving group SOCl 2 R CH 2H pyridine R CH 2l PBr3 R CH 2H ether R CH 2r  Mechanism of reacPBrn between 1° Alcohol and Thionyl Chloride R CH OH ether R CH Br 2 2  Advantages of SO2l Reagent i. Thionyl chloride (S2Cl ) converts OF to chlorosulfite ester, -OSOCl, a better leaving group ii. –OSOCl is pushed out as Cl is delivered 2 CHM247H1 Jasmyn Lee iii. The byproduct, SO , is2a gas that floats away – irreversible reaction Summary of Alkyl Halide Reaction Mechanisms O Basicity vs. Nucleophilicity _ _  Base reacts with H + H3C O H3C O
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