Migratory Aptitude Definition:

In a Baeyer- Villiger oxidation, the migration rates of different groups, which determine the regiochemical outcome of the reaction.

Migratory Aptitude Explained:

The migratory aptitude list for the Baeyer-Villager oxidation is as it is because that is how the molecules undergoing the reaction behave.

The migratory aptitude list (H>R3C>R2HC≈Ph(>H)>RCH2>Me)(H>RX3C>RX2HC≈Ph(>H)>RCHX2>Me)

Is the result of many experiments. Nor is it a linear list as is usually presented. HH migrates more readily than tertiary groups, which migrate more readily than secondary groups, which migrate more readily than phenyl groups (which migrate more readily than HH).