Examine the following pericyclic reactions. For each reaction, tell whether it is an electrocyclic reaction, a cycloaddition reaction, or a sigmatropic rearrangement.
a.
b.
c.
d.

Identify the type of following pericyclic reaction.

Identify the type of the following pericyclic reaction.

Identify the type of following pericyclic reaction.

Show that the [4 + 4] cycloaddition of two butadiene molecules to give cycloocta-1,5-diene is thermally forbidden but photochemically allowed.

Given the following reaction: ${\mathrm{1,3}}_{\mathrm{butadiene}}$ reacts with $\mathrm{ethene}$ to form $\mathrm{cyclohexene}$, what is the correct classification of this pericyclic reaction?

Identify the type of pericyclic reaction shown below: $C_{6}H{6}_6$ undergoes a reaction with heat to form $C_{6}H{6}_6$ with a new six-membered ring. What is this reaction called?