A rearrangement that can occur in some polymerization reactions involving free radicals. A radical that has an unpaired electron at the end of the chain changes into a radical with the unpaired electron elsewhere along the chain, the new radical being more stable than the one from which it originates. For example, the radical RCH2CH2CH2CH2CH2CH2· may change into RCH2CH·CH2CH2CH2CH3
The rearrangement is equivalent to a hydrogen atom being transferred within the molecule. The new unpaired electron initiates further polymerization, with the production of polymers with butyl (CH3CH2CH2CH2-) side chains.