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Pericyclic Reactions: Sigmatropic Rearrangements

Sigmatropic Rearrangements: Introduction

In [1,n] sigmatropic rearrangements, a residue (mostly a hydrogen atom) migrates from one end of a π system to the other.

Fig.1
Schematic representation
Fig.2
Examples

The nomenclature of [1,n] sigmatropic rearrangements derives from the position of the residue R before and after the reaction. For example, a [1,3] sigmatropic rearrangement describes a reaction in which the residue migrates from position 1 to position 3.

During the migration of the residue in [1,n] sigmatropic reactions shown above, one end of the σ bond remains attached to the rest of the molecule. However, there are cases in [n,m] sigmatropic rearrangements where both termini of the σ bond move:

Fig.3
Schematic representation
Fig.4
Examples
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