Illustrated Glossary of Organic Chemistry

1,3-Hydrogen shift or [1,3]-H shift: A sigmatropic rearrangement in which a hydrogen atom migrates to a new spot two atoms away from its starting spot, with simultaneous shift of a pi bond. While a [1,3]-H shift is symmetry-allowed by the Woodward-Hoffmann rules as a thermal, antarafacial shift, the required Mobius transition state geometry and orbitals available to a hydrogen atom prevent the shift.

This [1,3]-H shift in 1-butene is prevented by the transition state geometry requirements.

Concerted keto-enol tautomerization by [1,3]-H shift is prevented, so acid catalysis or base catalysis is required for tautomerization to occur.