Not all tautomers generated.

I drew each of three related tautomers in MarvinSketch (using the online version, which I believe is 5.3.8) and then selected Tools -> Isomers -> Tautomers -> All Tautomers. 

The three compounds are listed here as SMILES:

Compound A: O=C1CC(=NO1)C1=CC=CC=C1
Compound B: O=C1ONC(=C1)C1=CC=CC=C1
Compound C: OC1=CC(=NO1)C1=CC=CC=C1

When I input Compound A, the only tautomer found is Compound A.
When I input B, the only tautomer found is compound B.
When I input C, tautomers B & C are found.

Shouldn't all three tautomers be returned, regardless of which compound is used as the input?

 

Hi,

 

The ester group (A)  and the aromatic rings (B,C) are protected by the default settings of the tautomerization. This is why these fragments are excluded from the tautomerization.

Optionally , however, both the ester group and the aromatic ring can be activated in the tautomerization process if   the "Protect ester groups"  and the "Protect aromaticity" options are switched off on the options panel. See the attached figure.

 

Jozsi

Jozsi,

Thank you for the explanation.  I understand this better now.

Tim