9. Alkenes and Alkynes

Propose mechanisms for the following reactions.

(d)

Propose mechanisms for the following reactions.

(c)

Propose mechanisms for the following reactions.

(b)

Show the product(s) you expect from dehydration of the following alcohols when they are heated in sulfuric or phosphoric acid. In each case, use a mechanism to show how the products are formed.

(b)

The acid-catalyzed hydration we learned here in Chapter 8 is reversible.

(a) Propose a mechanism for the formation of an alkene from an alcohol.

The acid-catalyzed hydration we learned here in Chapter 8 is reversible:

(d) How might you shift the equilibrium to the right?

The acid-catalyzed hydration we learned here in Chapter 8 is reversible:

(e) How might you shift the equilibrium to the left?

If the compound shown in the margin is heated in the presence of H₂SO₄,

a. what constitutional isomer would be formed in greatest yield?

b. what stereoisomer would be formed in greater yield?

Explain why the acid-catalyzed dehydration of an alcohol is a reversible reaction, whereas the base-promoted dehydrohalogenation of an alkyl halide is an irreversible reaction.

What stereoisomers are formed in the following reactions? Which stereoisomer is the major product?

a. the acid-catalyzed dehydration of 1-pentanol to 2-pentene

Explain why the following alcohols, when heated with acid, form the same alkene.

When the following seven-membered ring alcohol is dehydrated, three alkenes are formed. Propose a mechanism for their formation.

When heated with H₂SO4, both 3,3-dimethyl-2-butanol and 2,3-dimethyl-2-butanol are dehydrated to form 2,3-dimethyl-2-butene. Which alcohol dehydrates more rapidly?

Write the appropriate reagent over each arrow.

What is the major product(s) of each of the following reactions?

d.