there is another way that a sigmatropic reaction can produce products with different sterochemistry. the migrating group can stay on the original face of the π system after rebonding. or, it can go to the opposite face of the π system. 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. transformations that occur within small- or medium-sized rings cannot make antarafacial shifts.