16. Conjugated Systems

a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.

1.

2.

b. Using arrows, show the electron rearrangement that takes place in each reaction.

1.

2.

A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the five-membered ring. Propose a mechanism to account for this observation.

Draw the product of each of the following sigmatropic rearrangements:

d.

Draw the product of each of the following sigmatropic rearrangements:

c.

Propose a mechanism for the following reaction:

If the compounds shown here are heated, one will form one product from a [1,3] sigmatropic rearrangement and the other will form two products from two different [1,3] sigmatropic rearrangements. Draw the products of the reactions.

What is the product of the following [1,3] sigmatropic rearrangement, A or B?

a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration?