08+ - P1: PBU/OVY JWCL234-08 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 JWCL234-08 JWCL234-Solomons-v1 December 9, 2009 16:42 CONFIRMING PAGES 8 ALKENES AND ALKYNES II: ADDITION REACTIONS SOLUTIONS TO PROBLEMS 8.1 CH 3 CHCH 2 I Br 2-Bromo-1-iodopropane 8.2 (a) + Br Br H δ + δ + Br (b) + Cl Cl I I δ + δ + Cl I (c) I H δ + δ + I I 8.3 (a) + Cl Cl Cl Cl H δ + δ + 1, 2-hydride shift 3 ° Carbocation 2 ° Carbocation 2-Chloro-2-methylbutane (from rearranged carbocation) + Cl + 2-Chloro-3-methylbutane (from unrearranged carbocation) Unrearranged 2 ° Carbocation 130
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-08 JWCL234-Solomons-v1 December 9, 2009 16:42 CONFIRMING PAGES ALKENES AND ALKYNES II: ADDITION REACTIONS 131 (b) + + 3-Chloro-2,2-dimethylbutane (from unrearranged carbocation) 2-Chloro-2,3-dimethylbutane (from rearranged carbocation) 1,2-methanide shift Cl + Cl H δ + δ Cl Cl Cl 8.4 CH 2 H 2 SO 4 CH 2 CH 3 CH 2 OSO 3 H + CH 3 CH 2 OH H 2 SO 4 + H 2 O heat 8.5 (a) (from dilute H 2 SO 4 ) + HH H O + + + H H O + H + O H 3 O + H + HO H H O (b) Use a high concentration of water because we want the carbocation produced to react with water. And use a strong acid whose conjugate base is a very weak nucleophile. (For this reason we would not use HI, HBr, or HCl.) An excellent method, therefore, is to use dilute sulfuric acid. (c) Use a low concentration of water (i.e., use concentrated H 2 SO 4 ) and use a higher temperature to encourage elimination. Distill cyclohexene from reaction mixture as it is formed, so as to draw the equilibrium toward product. (d) 1-Methylcyclohexanol would be the product because a 3 carbocation would be formed as the intermediate. + H O H + + + H H H + + H H H 3 O + + OH O O
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-08 JWCL234-Solomons-v1 December 9, 2009 16:42 CONFIRMING PAGES 132 ALKENES AND ALKYNES II: ADDITION REACTIONS 8.6 + methanide migration + + + OH O H H H H 2 O H + Ο H H H H H 3 O + + 8.7 The order reflects the relative ease with which these alkenes accept a proton and form a carbocation. (CH 3 ) 2 C CH 2 reacts faster because it leads to a tertiary cation, (CH 3 ) 2 C CH 2 H 3 O + CH 3 C + CH 3 CH 3 3 ° Carbocation CH 3 CH CH 2 leads to a secondary cation, H 3 O + CH 2 CH 3 CH CH 3 C + CH 3 H 2 ° Carbocation and CH 2 CH 2 reacts most slowly because it leads to a primary carbocation. H 3 O + CH 2 CH 2 CH 3 C + H H 1 ° Carbocation Recall that formation of the carbocation is the rate-determining step in acid-catalyzed hydration and that the order of stabilities of carbocations is the following: 3 > 2 > 1 > + CH 3 8.8 Me H + + H OSO 3 H OSO 3 H ( H 2 SO 4 ) H Me Me
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P1: PBU/OVY P2: PBU/OVY QC: PBU/OVY T1: PBU Printer: Bind Rite JWCL234-08 JWCL234-Solomons-v1 December 9, 2009 16:42 CONFIRMING PAGES ALKENES AND ALKYNES II: ADDITION REACTIONS 133 8.9 (a) (1) Hg(OAc) 2 / THF −Η 2 O (2) NaBH 4 , OH OH (b) (1) Hg(OAc) 2 /THF 2 O (2) NaBH 4 , OH (c) (1) Hg(OAc) 2 /THF 2 O (2) NaBH 4 , OH OH can also be used.
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08+ - P1: PBU/OVY JWCL234-08 P2: PBU/OVY QC: PBU/OVY T1:...

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