 In type 3 the substrates are epoxides, notably 2,3-epoxy-alcohols and type 4 concerns the reactions of alpha hydroxyketones and alpha hydroxy imines.Reactions of type 4 are also called acyloin rearrangements.While similar to the pinacol rearrangement, the semipinacol rearrangement differs from the pinacol rearrangement in that the cation is not formed from a vicinal 1,2-diol.