06+ - P1: PBU/OVY JWCL234-06 P2: PBU/OVY QC: PBU/OVY T1:...

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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-06 JWCL234-Solomons-v1 December 8, 2009 21:34 CONFIRMING PAGES 6 IONIC REACTIONS — NUCLEOPHILIC SUBSTITUTION AND ELIMINATION REACTIONS OF ALKYL HALIDES SOLUTIONS TO PROBLEMS 6.1 (a) cis -1-Bromo-2-methylcyclohexane (b) cis -1-Bromo-3-methylcyclohexane (c) 2,3,4-Trimethylheptane 6.2 (a) 3 (b) vinylic (c) 2 (d) aryl (e) 1 6.3 Substrate Nucleophile Leaving group I I O O CH 3 CH 3 CH 2 CH 3 CH 3 CH 2 ++ (a) Substrate Nucleophile Leaving group I Br Br CH 3 CH 2 CH 3 OH 2 CH 3 CH 2 I (b) Substrate Nucleophile Leaving group Cl Cl (CH 3 ) 3 C O (CH 3 ) 3 C 2 CH 3 OH CH 3 + (c) Substrate Nucleophile Leaving group CN Br C N (d) (e) Substrate Nucleophile Leaving group NH 4 + + + Br + + NH 2 Br Br 2 NH 3 85
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-06 JWCL234-Solomons-v1 December 8, 2009 21:34 CONFIRMING PAGES 86 IONIC REACTIONS 6.4 Free energy of activation Products Reactants Free- energy change I + Reaction coordinate Free energy Δ G ° Δ G Transition state CH 2 CH 2 CH 2 CH 3 Cl + I Cl Cl I δ− 6.5 I (CH 3 ) 3 C Br I + (CH 3 ) 3 C Br 6.6 (a) We know that when a secondary alkyl halide reacts with hydroxide ion by substitution, the reaction occurs with inversion of conFguration because the reaction is S N 2. If we know that the configuration of ( )-2-butanol (from Section 5.8C) is that shown here, then we can conclude that ( + )-2-chlorobutane has the opposite configuration. HO H OH S N 2 Cl H ( R )-( )-2-Butanol = − 13.52 [ α ] 25 ° D ( S )-( + )-2-Chlorobutane = + 36.00 [ α ] 25 ° D (b) Again the reaction is S N 2. Because we now know the configuration of ( + )-2-chlorobu- tane to be ( S ) [cf., part (a)], we can conclude that the configuration of ( )-2-iodobutane is ( R ). Cl H I S N 2 H I ( R )-( )-2-Iodobutane ( S )-( + )-2-Chlorobutane ( + )-2-Iodobutane has the ( S ) configuration.
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-06 JWCL234-Solomons-v1 December 8, 2009 21:34 CONFIRMING PAGES IONIC REACTIONS 87 6.7 (b) < (c) < (a) in order of increasing stability 6.8 (a) (b) H 2 O S N 1 I + (CH 3 ) 3 C (a, b) (CH 3 ) 3 C CH 3 OH 2 + A HA CH 3 By path (a) By path (b) + (CH 3 ) 3 C OH CH 3 (CH 3 ) 3 C CH 3 OH 6.9 and (CH 3 ) 3 C OCH 3 CH 3 (CH 3 ) 3 C CH 3 OCH 3 6.10 (c) is most likely to react by an S N 1 mechanism because it is a tertiary alkyl halide, whereas (a) is primary and (b) is secondary. 6.11 (a) Being primary halides, the reactions are most likely to be S N 2, with the nucleophile in each instance being a molecule of the solvent (i.e., a molecule of ethanol). (b) Steric hindrance is provided by the substituent or substituents on the carbon β to the carbon bearing the leaving group. With each addition of a methyl group at the β carbon (below), the number of pathways open to the attacking nucleophile becomes fewer. C H H H H H Br Nu H 3 C C H H H H Br Nu H 3 C H 3 C C H H H Br Nu H 3 C H 3 C H 3 C C H H Br Nu 6.12 CN > CH 3 O > CH 3 CO 2 > CH 3 CO 2 H > CH 3 OH Order of decreasing nucleophilicity in methanol
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-06 JWCL234-Solomons-v1 December 8, 2009 21:34 CONFIRMING PAGES 88
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This note was uploaded on 10/20/2011 for the course CHEMISTRY ES110 taught by Professor Te.li during the Spring '11 term at Central Texas College.

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06+ - P1: PBU/OVY JWCL234-06 P2: PBU/OVY QC: PBU/OVY T1:...

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