16. Conjugated Systems

Identify the type of the following pericyclic reaction.

Identify the type of following pericyclic reaction.

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?

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

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?

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.