If the migrating group remains on the same face of the π system , the shift is known as suprafacial , while if the migrating group transfers to the opposite face is called an antarafacial shift , which are impossible for transformations that occur within small - or medium-sized rings .
If the migrating group remains on the same face of the π system , the shift is known as suprafacial . If the migrating group transfers to the opposite face is called an antarafacial shift .