Editing Structural isomer (section)

===Structural equivalence===
Two molecules (including polyatomic ions) A and B '''have the same structure''' if each atom of A can be paired with an atom of B of the same element, in a one-to-one way, so that for every bond in A there is a bond in B, of the same type, between corresponding atoms; and vice versa.<ref name=mumb2018/> This requirement applies also to complex bonds that involve three or more atoms, such as the [[delocalized bond]]ing in the benzene molecule and other aromatic compounds.

Depending on the context, one may require that each atom be paired with an atom of the same isotope, not just of the same element.

Two molecules then can be said to be structural isomers (or, if isotopes matter, structural isotopomers) if they have the same molecular formula but do not have the same structure.