why can a ionization state not repeat itself?

I tried a simple molecule, O[N+]1=CC=CC=C1, on the pKa calculator using default parameters. it generated two states, (1) O[N+]1=CC=CC=C1 and (2) [O-][N+]1=CC=CC=C1, and result is listed in pKa_chart1. The first one repeats itself and the second one is a new ionization state.





I then took the second one as input structure and do the pKa calculation again. I was expecting it would generate exactly the same two structures as above , but it did not. It gave two new structures, (3) O=N1=CC=CC=C1 and (4) [OH+]=N1=CC=CC=C1, result is listed in pKa_chart2. When I did the same thing with (3) and (4), they all did right and repeated themselves.





My question is why structure (2) failed to repeat itself?

Hi,





You are right this is an up-to date problem of the pKa calculation. Some of the older forum topics already pointed out to the problem of the resonance structures.





Resonance is not handled correctly by the pKa calculator.





Structure (1) is not calculated correctly. See the attached picture.





We are working on the solution of this problem.








Jozsi