15%20Ch09 - CHAPTER 9 Elimination Reactions of Alkyl...

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275 CHAPTER 9 Elimination Reactions of Alkyl Halides • Competition Between Substitution and Elimination Important Terms anti elimination an elimination reaction in which the substituents being eliminated are removed from opposite sides of the molecule. anti-periplanar substituents are parallel on opposite sides of a molecule. dehydrohalogenation elimination of a proton and a halide ion. deuterium kinetic ratio of the rate constant obtained for a compound containing hydrogen isotope effect and the rate constant obtained for an identical compound in which one or more of the hydrogens have been replaced by deuterium. elimination reaction a reaction that removes atoms or groups from the reactant to form a π bond. β -elimination reaction an elimination reaction where the groups being eliminated are bonded to or adjacent carbons. 1,2-elimination reaction E1 reaction a unimolecular elimination reaction. E2 reaction a bimolecualr elimination reaction. regioselectivity the preferential formation of a constitutional isomer. sawhorse projection a way to represent the three-dimensional spatial relationships of atoms by looking at the carbon-carbon bond from an oblique angle. syn elimination an elimination reaction in which substituents being eliminated are removed from the same side of the molecule. syn-periplanar substituents are parallel on the same side of a molecule. target molecule the desired end product of a synthesis. Williamson ether formation of an ether from the reaction of an alkoxide ion with an alkyl synthesis halide. Zaitsev’s rule the rule that states that the more stable alkene product is obtained by removing a proton from the -carbon that is bonded to the fewest hydrogens.
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276 Chapter 9 Solutions to Problems 1. CH 3 CC H C H 3 CH 3 a. CH 3 H C H 3 CH 3 b. CH 3 CH 2 CCH c. CH 3 CH 3 CH 2 2. a. CH 3 CH 2 CHCH 3 Br The alkene that is formed is more stable than the alkene that is formed from the other alkyl halide. b. Br Br is a better leaving group (weaker base) than Cl. c. CH 3 CH 2 CH 2 CCH 3 Br CH 3 The alkene that is formed is more stable than the alkene that is formed from the other alkyl halide. d. CH 3 CCH 2 CH 2 Cl CH 3 CH 3 The other alkyl halide cannot undergo an E2 reaction because it doesn’t have any β -hydrogens. 3. The reaction of 2-bromo-2,3-dimethylbutane with sodium tert -butoxide forms two alkene elimination products. Because of steric hindrance, the less stable alkene (2,3-dimethyl-1-butene) is the one that is easier to make. CH 3 H C H 3 CH 3 Br CH 3 (CH 3 ) 3 CO CH 2 C CH 3 CHCH 3 CH 3 + CH 3 C H 3 CH 3 CH 3 2-bromo-2,3-dimethylbutane 2,3-dimethyl-1-butene 2,3-dimethyl-1-butene
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Chapter 9 277 4. a. 33 CH CH CHCH Removal of a β - hydrogen from the most substituted carbon forms the most stable “alkene-like” transition state.
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This note was uploaded on 03/29/2010 for the course CHE 118A 118a taught by Professor Kent during the Spring '10 term at UC Davis.

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15%20Ch09 - CHAPTER 9 Elimination Reactions of Alkyl...

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