According to this oversimplified principle, chemical species do not isomerize in the course of a transformation, e.g. substitution, or the change of a functional group of a chemical species into a different functional group is not expected to involve the making or breaking of more than the minimum number of bonds required to effect that transformation. For example, any new substituents are expected to enter the precise positions previously occupied by displaced groups.[1] Molecular rearrangements[2] violates the so-called 'principle of minimum structural change'. References: IUPAC Goldbook, doi:10.1351/goldbook.M03997 The term is traditionally applied to any reaction that involves a change of connectivity (sometimes including hydrogen)