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Sigmatropic Reactions

This guide is an early version — the text is complete, and a few figures are still being redrawn. Spotted something unclear? Let us know.

The question this page answers: What are the characteristics of sigmatropic reactions?

Deeper reading: Clayden 2e: Chapter 35 Pages 909–922 — see our chapter-by-chapter practice map for Clayden.

Part of the Pericyclic Reactions overview.

The [x, y] nomenclature

What do the numbers in [1, 5] mean?

Nomenclature for sigmatropic reactions describes them as being [x, y] processes.

In the [x, y] nomenclature, the x and y describe the position of the atoms in the new σ bond relative to the original σ bond’s location, which is designated as [1, 1]:

In the [x, y] nomenclature, the x and y describe the position of the atoms in the new σ bond relative to the original σ bond’s location, which is desi

Allowed sigmatropic shifts

Which sigmatropic shifts are allowed?

A simplified consideration of MOs is to look at the LUMO of the π system and the HOMO of the group that is “moving”.

Here are the Woodward-Hoffmann Rules for allowed sigmatropic processes:

Here are the Woodward-Hoffmann Rules for allowed sigmatropic processes:

Here are some examples for hydride shifts:

Here are some examples for hydride shifts:

Here is an example for a methyl shift in which the methyl group is inverted:

Here is an example for a methyl shift in which the methyl group is inverted:

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