Exact matches or tautomers?

[From a user email...]





Why do the following structures match each other using an exact search in JChem? I appreciate the fact that all rings are fully aromatic, but the N hydrogen position varies between the structures. I believe the structures are tautomers, not exact matches.

Please note that for deciding the equality of molecules you should use the PERFECT search mode.





EXACT matching means that the atom graphs are corresponding to each other. In this mode the matching works exactly as substructure search, but the number of atoms in the two molecules (not including implied H-s) must be the same.





You can also differentiate the structures with EXACT searching if you add explicit hydrogens to the aromatic N of the query.





See the relevant sections of the Query Guide:





http://www.jchem.com/doc/user/Query.html#explH


http://www.jchem.com/doc/user/Query.html#otherSearchTypes





In the future we will provide tautomeric searching, too.





Best regards,


Szabolcs