NMR-prediction problems for mesomeric resonance systems

User 25d107bd42

14-11-2012 20:06:10

Hi,


once more the Marvin programs have problems with mesomeric pi-systems (resonance systems).


For the attached pentacyanin-cation the NMR-calculations give different results for three important resonance structures. It's a very old problem. For HMO and other calculations has been solved. Now we have in the new NMR calculation method.


The problem is also for other conjugated mesomeric polymethin dyes, such as phenolphthalein anion or Capri blue cation. In the next post there is one example more.


Are these problems solved in the coming version 5.11.4, too ?


Best regards, Hans-Ulrich

User 25d107bd42

14-11-2012 20:47:05

Hi,


here attached the next example: Bindschedlers Green. The cation has C2v symmetry, but one ring is recognized "aromatic" and the other not. And the NMR shift values are different, too.


Best regards, Hans-Ulrich

ChemAxon f6a6029129

16-11-2012 15:26:50

Dear Hans-Ulrich,


this issue still exists in Marvin 5.11.4. But the problem is clear and we will solve it in the future.


Best regards,


Csaba

User 25d107bd42

16-11-2012 16:40:54

Dear Csaba,


thank you for your informations. It seems to me, to manage those molecules and ions in HMO calculations was easier as for your NMR simulations. But this leads to an idea: Perhaps the charge results of those HMO calculations are a contribution to your simulation parameters. I remember some time ago we used these HMO charges to find the assignment of experimental NMR results.


The HMO charge results show at least the conjugation effects and the symmetry of those conjugated systems.


Best regards, Hans-Ulrich