1559T_ch19_344-35710/17/0513:51Pa9e35 ⊕ EQA Solutions to Problems.353 38.As usual,think mechanistically.The first intermediate should be the cyclic bromonium ion: OH Ag.base r Br The bromolactones shown are formed by intramolecular attack by a carboxylate oxyger n on one of the for two reasons.First.attack bya nucleophile on a brominium ion normally takes place at the atom (whi amic edge th hered rings have B 39.(CH,CH.,CH.CHCOOH viaCH.CH,CH.CBr -CH;CH,CH=C-Br Br-CBr_ CH,CH,CHBrCBr Then Br NH, CH,CH.CHCOOH+NHCH,CH.CHCOOH Product CN product (e)CH;CH,CH(CH)CH:CH.COOHP The t0. product Solutions to Problems • 353 36. 1. LiAlH4, (CH3CH2)2O (makes 1-pentanol); 2. KBr, H2SO4, ; 3. KCN, DMSO (makes hexanenitrile); 4. KOH, H2O, ; 5. H, H2O, 37. (a) SOCl2; (b) H, CH3OH; (c) H, 2-butanol; (d) alkanoyl chloride from (a); (e) CH3NH2 (via the ammonium salt), ; (f) LiAlH4, (CH3CH2)2O; (g) Br2, cat. P 38. As usual, think mechanistically. The first intermediate should be the cyclic bromonium ion: The bromolactones shown are formed by intramolecular attack by a carboxylate oxygen on one of the carbon atoms of a cyclic bromonium ion, the initial product of Br2 addition to the double bond (Section 12-6). Which pathway, a or b, should be favored? The five-membered ring should form preferentially, for two reasons. First, attack by a nucleophile on a brominium ion normally takes place at the more highly substituted carbon atom (which is more positively polarized—see Section 12-6 again). Second, five-membered rings form faster than do sixes (Section 9-6), compensating for the slight thermodynamic edge that six-membered rings have. 39. (a) Then (b) (c) CH3CH2CH(CH3)CH2CH2COOH Br2, cat. P product 1. K2CO3, H2O, 2. H, H2O Then CH2CO2H 1. Br2, cat. P 2. KCN, DMSO CHCO2H product 1. HO, H2O 2. H, H2O CN CH3CH2CHCOOH CH NH3 3CH2CHCOOH product NH3 Br SN2 H Br O exchange CH3CH2CHBrCBr . via CH3CH2CH2CBr CH3CH2CH O C Br Br Br O H CH3CH2CH2COOH CH3CH2CHCOOH Br2, cat. P Br O O O Br Br O O O OH Aq. base a a b or or b Br O  Br 1559T_ch19_344-357 10/17/05 13:51 Page 353