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468 CHAPTER 13 
 
ejected as a leaving group, giving the cyclic product 
shown: 
 
 
13.39. The starting material is a cyclic ether, in which 
the oxygen atom is connected to two carbon atoms, each 
of which is sp3 hybridized. As such, treatment with HBr 
is expected to cleave each of the CO bonds and replace 
them with CBr bonds, giving the following dibromide: 
 
 
 
 
13.40. The starting material has six carbon atoms, and 
the product has six carbon atoms. So, the starting 
material must be some sort of cyclic ether, which opens 
to give a dibromide. By inspecting the dibromide 
product, we can determine which two carbon atoms must 
have been connected to the oxygen atom in the starting 
cyclic ether. 
 
 
 
 
 
 
13.41. Ethyl magnesium bromide is a strong nucleophile, and can attack the epoxide at the less substituted position, in 
a ring-opening process, with inversion of configuration at the position that is attacked. The resulting alkoxide ion can 
then undergo an intramolecular SN2-type process, expelling a chloride ion and generating a new epoxide. This epoxide 
can be attacked once again by ethyl magnesium bromide, once again at the less substituted position, and once again 
with inversion of configuration. The resulting alkoxide ion is then protonated upon treatment with water, to give the 
observed product. 
 
 
 
 
 
 
13.42. 
(a) The starting material is an alkene, and the reagents 
indicate an alkoxymercuration-demercuration, resulting 
in the Markovnikov addition of H and OMe across the  
bond. 
 
 
 
(b) The starting material is an alkene, and the reagents 
indicate an alkoxymercuration-demercuration, resulting 
in the Markovnikov addition of H and OR across the  
bond. 
 
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