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CHAPTER 8 259 
 
alkene, so we must use a strong base that is not sterically 
hindered, such as methoxide (hydroxide or ethoxide can 
also be used). 
 
2) NaOMe
1) HBr
 
 
 
(b) This trisubstituted alkene can be converted into the 
monosubstituted alkene via a two-step process (addition, 
followed by elimination). We must be careful to control 
the regiochemical outcome of each of these steps. 
During the addition process, we want to install Br at the 
less-substituted (secondary) position, so we treat the 
alkene with HBr in the presence of peroxides. Then, the 
elimination process must be performed in a way that 
gives the less-substituted alkene, so we must use a 
strong, sterically hindered base (such as tert-butoxide). 
 
 
 
 
 
8.47. Treatment of the starting alcohol with concentrated 
sulfuric acid affords the more substituted alkene. 
Moving the position of the  bond can then be achieved 
via a two step-process (addition, followed by 
elimination). We must be careful to control the 
regiochemical outcome of each step of the process. 
During the addition reaction, we want to install Br at the 
less-substituted (secondary) position, so we treat the 
alkene with HBr in the presence of peroxides. Then, the 
elimination reaction must be performed in a way that 
gives the less-substituted alkene, so we must use a 
strong, sterically hindered base (such as tert-butoxide). 
 
 
 
 
 
8.48. Two different alkenes will produce 2,4-
dimethylpentane upon hydrogenation: 
 
 
H2
Pt
H2
Pt 
 
Note that the following four drawings all represent the 
same compound: 
 
 
 
 
8.49. We must first determine the structure of 
compound A. The necessary information has been 
provided. Specifically, ozonolysis of compound A gives 
only one product, which has only one C=O bond. 
Therefore, the starting alkene must be symmetrical, 
leading to two equivalents of the product: 
 
 
Treatment of compound A with a peroxy acid, followed 
by aqueous acid, affords a diol. No chiral centers are 
formed, so stereochemistry is not a relevant 
consideration. 
 
 
8.50. 
(a) Interconversion between the two alcohols requires 
moving the position of the OH group. In each case, this 
can be accomplished via a two step-process (elimination 
followed by addition). In each case, the elimination step 
can be achieved by treating the alcohol with concentrated 
sulfuric acid. For the addition step, the regiochemical 
outcome must be carefully considered. In the first case 
below, dilute aqueous acid is used to give a 
Markovnikov addition, while in the second case below, 
hydroboration-oxidation is employed to give an anti-
Markovnikov addition. 
 
 
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