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.