16. Conjugated Systems

a. When HBr adds to a conjugated diene, what is the rate-determining step?

b. When HBr adds to a conjugated diene, what is the product-determining step?

What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction? Disregard stereoisomers.

a.

Whereas stabilized enolates do 1,4-addition, unstabilized (normal) enolates can do both 1,2- and 1,4-addition depending on the situation. Why might this be?

When Br₂ is added to buta-1,3-diene at –15 °C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 60 °C, the product ratio is 10% A and 90% B.

d. If you had a solution of pure A, and its temperature were raised to 60 °C, what would you expect to happen? Propose a mechanism to support your prediction.

What products would be obtained from the reaction of 1,3,5-hexatriene with one equivalent of HBr? Disregard stereoisomers.

What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction?

a.

Would you expect the following nucleophiles to do 1,2- or 1,4-addition?

(d)

(e)

(f)

What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction?

c.

What are the products of the following reaction?

Draw the major products obtained from the reaction of one equivalent of HBr with the following compounds. For each reaction, indicate the kinetic product and the thermodynamic product.

b.

Predict the products of the following reactions.

(e) buta-1,3-diene + bromine water

a. How could each of the following compounds be prepared from a hydrocarbon in a single step?

b. What other organic compound would be obtained from each synthesis?

1.

Draw the major products obtained from the reaction of one equivalent of HCl with the following compounds. For each reaction, indicate the kinetic and thermodynamic products.

a. 2,3-dimethyl-1,3-pentadiene