16. Conjugated Systems

What are the major 1,2- and 1,4-addition products of the following reaction? Indicate the kinetic and the thermodynamic products.

a.

Predict the products of the following reactions.

(f) hexa-1,3,5-triene + bromine in CCl₄

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

(a)

(b)

(c) HO^–

How many stereoisomers of each product could be obtained?

Predict the product of the following addition reactions to dienes.

(a)

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?

2.

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

b.

The experiment shown next and discussed in Section 8.13 shows that the proximity of the chloride ion to C-2 in the transition state causes the 1,2-addition product to form more rapidly than the 1,4-addition product.

a. Why was it important for the investigators to know that the preceding reaction was being carried out under kinetic control?

Propose a mechanism for each reaction, showing explicitly how the observed mixtures of products are formed.

c. cyclopenta-1,3-diene + Br₂ → 3,4-dibromocyclopent-1-ene + 3,5-dibromocyclopent-1-ene

Predict the products of the following reactions.

(b) cyclopentadiene + anhydrous HCl

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

(g)

(h)

(i)

When 1 mole of buta-1,3-diene reacts with 1 mole of HBr, both 3-bromobut-1-ene and 1-bromobut-2-ene are formed. Propose a mechanism to account for this mixture of products.