Tautomer bonds used in some systems. For example, carboxylate oxygens
are chemcially equivalent, even though they are represented differently
in SMILES.
CC(=[O:1])[OH:1].ClS(=O)Cl>>CC(=[O:1])Cl
Ambiguities in reaction mechanism.
Maps can be used to express the overall reactions in multi-step
processes.
[CH2:1]=[CH:2][CH2:1][CH2:3][C:4](C)[CH2:3]
Incomplete information.
It is never acceptable to force a user to "make up" data in
order to register a reaction.
