1559r.ah12.220-24611/02/0521:55Page227 Solutions o Problems227 c nation from the more exposed (bottom)side of the folded 30.Mor 3 90° 19).The greater strain in cyclobutene tane,thus resulting in greater energy release upor 31 (i)Peroxide-free HBr (i HBr+ (Markovnikov addition) (anti-Markovnikov addition) (a)2-Bromohexane 1-Bromohexane (b)2-Bromo-2-methylpentane 1-Bromo-2-methylpentane (c)2-Bromo-2-methylpentane 3-Bromo-2-methylpentane (d)3-Bromohexane 3-Bromohexane All chiral products are formed as racemic mixtures. 32.(a)1.2-Dibromohexane (b)1.2-Dibromo-2-methylpentanc (c)2.3-Dibromo-2-methylpentanc Br H H Br Br H R一HBr Br R-= R Br Racemic mixture RC-C Meso compou (e)trans-1.2-Dibromocyclohexan All products in this problem (except for the meso compound)are chiral:all are racemicSolutions to Problems • 227 (c) Hydrogenation occurs from the more exposed (bottom) side of the folded molecule. 30. More exothermic. There is essentially no bond angle strain in either cyclohexane or cyclohexene. Heat of hydrogenation of the latter is essentially the same as that for an acyclic cis-disubstituted alkene. Both cyclobutane and cyclobutene are strained, but bond angle compression is greater in the alkene (120°  90° 30°) compared with the alkane (109°  90° 19°). The greater strain in cyclobutene increases the energy difference between it and cyclobutane, thus resulting in greater energy release upon hydrogenation. 31. (i) Peroxide-free HBr (ii) HBr
peroxides (Markovnikov addition) (anti-Markovnikov addition) (a) 2-Bromohexane 1-Bromohexane (b) 2-Bromo-2-methylpentane 1-Bromo-2-methylpentane (c) 2-Bromo-2-methylpentane 3-Bromo-2-methylpentane (d) 3-Bromohexane 3-Bromohexane (e) Bromocyclohexane Bromocyclohexane All chiral products are formed as racemic mixtures. 32. (a) 1,2-Dibromohexane (b) 1,2-Dibromo-2-methylpentane (c) 2,3-Dibromo-2-methylpentane (d) (R,R) and (S,S)-3,4-Dibromohexane. Anti addition to a cis compound gives a racemic mixture of chiral products; a trans substrate gives the meso isomer. (e) trans-1,2-Dibromocyclohexane All products in this problem (except for the meso compound) are chiral; all are racemic. Br Br H R R H C C Br Br Br H H Racemic mixture Meso compound R R R C C Br Br H R H R C C Br Br H H R R C C Br Br H H R R C C Br Br H H R C C R Br H H R C C H CH2 H H H 1559T_ch12_220-246 11/02/05 21:55 Page 227