91Ó°ÊÓ

Question: Using cis- and trans-hex-3-ene, demonstrate that the addition of HCl is not a stereospecific reaction. Draw the structure of the stereoisomers formed from each alkene.

Question: Draw a stepwise mechanism for the following reaction.

Question: Draw a stepwise mechanism for the following reaction, which results in ring expansion of a six-membered ring to a seven-membered ring.

Question: Draw a stepwise mechanism for the conversion of hex-5-en-1-ol to the cyclic ether A.

Question: Draw a stepwise mechanism that shows how all three alcohols are formed from the bicyclic alkene.

Question: Less stable alkenes can be isomerized to more stable alkenes by treatment with strong acid. For example, 2,3-dimethylbut-1-ene is converted to 2,3-dimethylbut-2-ene when treated with . Draw a stepwise mechanism for this isomerization process.

Question: When buta-1,3-diene (CH₂=CH-CH=CH₂) is treated with HBr, two constitutional isomers are formed CH₃CHBr-CH=CH₂and Br-CH₂CH=CHCH₂. Draw a stepwise mechanism that accounts for the formation of both products.

Question: Explain why the addition of HBr to alkenes A and C is regioselective, forming addition products B and D, respectively.

Question: Bromoetherification, the addition of the elements of Br and OR to a double bond, is a common method for constructing rings containing oxygen atoms. This reaction has been used in the synthesis of the polyether antibiotic monensin (Problem 21.37). Draw a stepwise mechanism for the following intramolecular bromoetherification reaction.

Question: Devise a synthesis of each product from the given starting material. More than one step is required.

a.

b.

c.

d.

e.

f.