Canonical tautomers

User dfbaf76535

17-02-2009 11:27:31

Hello everybody,





Can someone help me by understanding what are canonical tautomers? I know about the canonical smiles but what about tautomers? Is this just their representation into smile format?





thank you in advance.





Sylvain

User 851ac690a0

18-02-2009 00:07:51

Hi,








 For example:





 6 tautomers are depicted on the attached figure.  





 The same canonical tautomer "O=C1NNNC(=O)C1=O"


 will be assigned to the 6 structures. 





 Generation of the canonical tautomer based on empirical chemical rules.








Jozsi

User dfbaf76535

18-02-2009 07:43:40

Thank you Jozsi,





So, if I well understood what you mean, the canoninal tautomer is in fact the canonical smile of the reprensentation of all the tautomers?





I have another question: are there great differences between canonical tautomers, dominant tautomers and moststable tautomers? I succeeded to create the two first types. But I had many troubles in creating the last one. Can anybody help?





Sylvain

User 851ac690a0

18-02-2009 11:46:02

Hi,





Quote:
So, if I well understood what you mean, the canoninal tautomer is in fact the canonical smile of the reprensentation of all the tautomers?






    The canonical tautomer will be generated as a canonical smile if you specify the





    "-f  smiles:u"  option





          For example with the cxcalc command line,











Code:
cxcalc  "OC1=NN=NC(O)=C1O" canonicaltautomer  -f smiles:u









         And the generated canonical smile representation will be this:





         "O=c1[nH][nH][nH]c(=O)c1=O"














Quote:
I have another question: are there great differences between canonical tautomers, dominant tautomers and moststable tautomers? 









  • The canonical tautomer generation based on an empirical rule system that is applied to    the submitted molecule.Different tautomers always have the same canonical tautomeric forms.



  • The most stable tautomer generation based on a more complicated calculation since the   pKa values of the submitted molecule also invoked in the calculation.Because of the   pKa criteria  it can occure that different tautomers may have different most stable tautomeric forms.



  • The dominant tautomer distribution based on the calculation of the tautomeric equilibrium among alternative tautomeric forms. Distribution of tautomrers given in [%].






   


Jozsi

User dfbaf76535

18-02-2009 13:13:01

Hi,





What an answer! Thank you for all Jozsi.





Sylvain