1559T_ch04_55-6910/22/0520:19Page67 EQA Solfions to Problems67 The H-C-H bond ngl ld look like thi In reality.yclobutane uses"bent"bonds just like those of cyclopro ane.and all four bonds to each carbor H bond angle is not odecane is essentially the same do-co. The resulting molecule has these two new hydroge transannular interaction makes this a very high energy conformation. (b)All are trans. c)o means below and mean sabove.Therefore.3o-OH.4a-CHs.8a-CHs.10B-CH3.1la-OH .in-oo steroids have only chair and 10.and alsc o at positi at positions 4.8.10.and 14.instead of the more common pair of methyl groups at 1o and I OH -96kc Overal,△r 44.(a)Propagation CI+RH HCI+R. Can happen initially i-c The HOCOH bond angle would be 180° and cyclobutane would look like this: In reality, cyclobutane uses “bent” bonds just like those of cyclopropane, and all four bonds to each carbon involve hybridized orbitals. In addition, cyclobutane is not flat at all, and the HOCOH bond angle is not much different from the normal tetrahedral value of 109° (see Figure 4-3). 41. Notice that making “all-chair” cyclodecane is essentially the same as removing the ring-fusion bond from trans-decalin and replacing it with two hydrogens—one on each former ring-fusion carbon: The resulting molecule has these two new hydrogens pointing into the center of the ring, in prohibitively close contact with the carbon and hydrogens on the opposite side of the ring. The steric strain of this transannular interaction makes this a very high energy conformation. 42. (a) From left to right: chair cyclohexane, boat (or twist-boat) cyclohexane, chair cyclohexane, envelope cyclopentane. (b) All are trans. (c)  means below and  means above. Therefore, 3-OH, 4-CH3, 8-CH3, 10-CH3, 11-OH, (d) The boatlike cyclohexane ring is the most unusual feature; most steroids have only chair cyclohexanes. The boat shape is a result of the unusual cis relationship of the groups at positions 9 and 10, and also at positions 5 and 8. Note also the unusual number and location of methyl groups: at positions 4, 8, 10, and 14, instead of the more common pair of methyl groups at 10 and 13. 43. For (a), H° 98.5
102.5
4.0 kcal mol
1 ; for (b), H°
96 kcal mol
1 . Overall, H°
100 kcal mol
1 . 44. (a) Propagation: R· ICl2 RCl I Cl Cl· R· · RH HCl I Cl RH HCl R· I · Can happen initially Main steps of chain reaction OH O (a) HO· (b) · 14-CH3, 16 O OCCH3. H H H H H H H H Add Remove two H· bond H H H H H H H H Solutions to Problems • 67 1559T_ch04_55-69 10/22/05 20:19 Page 67