Addition of a functional group to the pro-R carbon of glycerol places that group on carbon _ while addition of a second functional group to the pro-S carbon of glycerol places the second group on carbon _ of sn-glycerol.

Question

Addition of a functional group to the pro-R carbon of glycerol places that group on carbon _____ while addition of a second functional group to the pro-S carbon of glycerol places the second group on carbon _____ of sn-glycerol.