Question: What type of pericyclic reaction is illustrated in each reaction?

The pericyclic reactions that involve the conversion of a sigma bond to a pi bond or vice-versa are known as electrocyclic reactions.

The reactions that involve the migration of a sigma bond followed by the delocalization of a pi bond are known as sigmatropic rearrangement reactions.

The pericyclic reactions involved in the given reactions are as follows.

Electrocyclic reaction

The given reaction involves the electrocyclic ring-opening.

Sigmatropic rearrangement

The given reaction involves a [1,2] hydrogen shift and, therefore, is a sigmatropic reaction.

Electrocyclic ring closure

The given reaction is an electrocyclic ring-closure reaction.