Chapter 30.SE, Problem 36AP

Interpretation Introduction

Interpretation:

The observation that photolysis of cis-cyclobutene yields cis-cyclododecaen-7-yne but photolysis of trans-cyclobutene yields trans-cyclododecaen-7-yne is to be explained by identifying the type and stereochemistry of the pericyclic reaction involved.

Concept introduction:

An electrocyclic reaction involves the cyclization of a conjugated acyclic system. These reactions are reversible and are highly stereospecific.

In elecrocyclic reactions involving even number of electron pairs, a thermal reaction occurs in conrotatory manner and a photochemical reaction occurs in disrotatory manner.

In elecrocyclic reactions involving odd number of electron pairs, a thermal reaction occurs in disrotatory manner and a photochemical reaction occurs in conrotatory manner.