Migratory aptitude
Migratory aptitude is the relative ability of a migrating group to migrate in a rearrangement reaction.{{cite web | url = https://goldbook.iupac.org/terms/view/M03923 | title = Migratory aptitude | work = Compendium of Chemical Terminology | publisher = International Union of Pure and Applied Chemistry }} Migratory aptitudes vary in different reactions, depending on multiple factors.{{Cite web | url = https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/rearrang.htm | title = Rearrangements Induced by Cationic or Electron Deficient Sites | author = William Reusch | publisher = Michigan State University }}
In the Baeyer-Villiger reaction, the more substituted group, in general, migrates.{{Cite web | title = Migratory Aptitudes | url = http://www.chem.ox.ac.uk/vrchemistry/nor/notes/migrapt.htm | publisher = Department of Chemistry, University of Oxford }} In the pinacol rearrangement, the order of migratory aptitude has not been determined unambiguously, but some trends have been determined. For example, relative migratory aptitudes for alkyl substituents is Hydride >C(CH3)3> C2H5 > phenyl > CH3.
More bulky groups have more tendency to migrate.