9. Alkenes and Alkynes

Write a balanced equation for each reaction, showing the major product you expect.

(a)

Write a balanced equation for each reaction, showing the major product you expect.

(c)

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.

(c)

Write a mechanism that explains the formation of the following product. In your mechanism, explain the cause of the rearrangement, and explain the failure to form the Zaitsev product.

Predict the products of the sulfuric acid-catalyzed dehydration of the following alcohols. When more than one product is expected, label the major and minor products.

(d) 1-isopropylcyclohexanol

(e) 2-methylcyclohexanol

Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.

(b)

Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.

(c)

Predict the product of the following pinacol rearrangements.

(b)

Propose a mechanism for each of the following reactions:

b.

Propose a mechanism for each of the following reactions:

a.

Propose a mechanism for each reaction.

(a)

(b)

Suggest an alkene that, in two steps, could be converted into each of the following ketones. Each sequence should involve a pinacol rearrangement.

(c)

The following reaction is called the pinacol rearrangement. The reaction begins with an acid-promoted ionization to give a carbocation. This carbocation undergoes a methyl shift to give a more stable, resonance-stabilized cation. Loss of a proton gives the observed product. Propose a mechanism for the pinacol rearrangement.

Treatment of the following alcohol was expected to give alkene A. Instead, B was produced as the major product. Suggest a mechanism by which B formed.

Although 2-methyl-1,2-propanediol is an unsymmetrical vicinal diol, only one product is obtained when it is dehydrated in an acidic solution.

a. What is this product?