16. Conjugated Systems

Draw the product of each of the following reactions:

d.

Draw the product of each of the following reactions:

e.

Draw the product of each of the following reactions:

f.

Explain why two different products are formed from disrotatory ring closure of (2E,4Z,6Z)-octatriene, but only one product is formed from disrotatory ring closure of (2E,4Z,6E)-octatriene.

cis-3,4-Dimethylcyclobutene undergoes thermal ring opening to form the two products shown. One of the products is formed in 99% yield, the other in 1% yield. Which is which?

If isomer A is heated to about 100 °C, a mixture of isomers A and B is formed. Explain why there is no trace of isomer C or D.

b. What would be the product if trans-2-butene were used instead of ethene?

Predict the product of the following electrocyclic reactions.

(a)

Draw the products you’d expect to form in Assessment 22.38.

(c)

Predict the product of the following reactions. [When all of the reactions from this chapter are shown together, you must first decide which type of reaction each is. Is it a Diels–Alder, an electrocyclic, or a sigmatropic rearrangement? Drawing the product will be easier once this determination is made.]

(b)