text:  <unk> have been found to undergo rearrangement reactions via a radical mechanism when irradiated with UV light or in the presence of a single electron transfer reagent such as <unk> <unk> <unk> undergo ring expansions to the corresponding lactam . Interestingly , the migrating substituent is determined by a <unk> effect where the group trans to the lone pair on the nitrogen will always be the predominant migration product . In light of this effect , it is possible to take advantage of the chiral nitrogen due to high inversion barrier to direct the rearrangement . This phenomenon is demonstrated by observed <unk> in the rearrangements below . In the rearrangement on the left the thermodynamically unfavorable product is observed exclusively , while in the reaction on the right the product derived from the less stable radical intermediate is favored . 
  