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

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.

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

Account for the difference in the products obtained under photochemical and thermal conditions:

Does the [1,7] sigmatropic rearrangement that converts provitamin D₃ to vitamin D₃ involve suprafacial or antarafacial rearrangement?

Choose the product most likely to form during the following sigmatropic rearrangement: A molecule of $1_3$-butadiene undergoes a ${[}_{\mathrm{3,3}}$] sigmatropic rearrangement (Claisen rearrangement). Which of the following is the major product?