Chapter 30.SE, Problem 39AP

Interpretation Introduction

Interpretation:

Whether the reaction shown, a [2,3] sigmatropic rearrangement, takes place through a suprafacial or antarafacial shift is to be explained.

Concept introduction:

Sigmatropic rearrangements involve the migration of a σ bond present at the end or in the middle of the system across the π electron system from one position to another. They are represented by [m,n] where m and n represents the number of atoms between the bond being broken and the bond being formed in two directions.

If even number of electron pair is involved then thermal reaction occur through antarafacial pathway and photochemical reactions occur through suprafacial pathway.

If odd number of electron pair is involved then thermal reaction occur through suprafacial pathway and photochemical reactions occur through antarafacial pathway.