User 25d107bd42
26-01-2009 10:33:43
Hi, there are more problems with resonance formulas describing one molcule/ion, here a dianion.
The dianion shown in the attached screenshots is described in the paper L.L.Miller et.al. J Amer Chem Soc 1990, 112, 1206. The dianion has D2h symmetry and cannot be formulated with only one resonance formula (like f.e. polymethine cyanine salts). Of the four major resonance formulas one can draw two are shown in the upper part of the screenshot (The other two are symmetry related).
The lower parts of the screenshots show the effect of "aromatization". Neither the "General aromatization" nor the "Basic aromatization" correspond to the symmetry of the dianion.
Calculations for this dianion give different results for these two resonance formulas describing the same dianion. In the screenshot are the different "Conformers Dreiding energies". Also other calculation tools, f.e. "Charge", "Protonation", "logP" and "Steric Hindrance" give different results.
The Marvin Huckel calculation tool is able to handle the pi-system of this dianion in correct D2h symmetry, both resonance formulas give the same result, see second screenshot bf0495.
What's wrong?
Regards, Hans-Ulrich
The dianion shown in the attached screenshots is described in the paper L.L.Miller et.al. J Amer Chem Soc 1990, 112, 1206. The dianion has D2h symmetry and cannot be formulated with only one resonance formula (like f.e. polymethine cyanine salts). Of the four major resonance formulas one can draw two are shown in the upper part of the screenshot (The other two are symmetry related).
The lower parts of the screenshots show the effect of "aromatization". Neither the "General aromatization" nor the "Basic aromatization" correspond to the symmetry of the dianion.
Calculations for this dianion give different results for these two resonance formulas describing the same dianion. In the screenshot are the different "Conformers Dreiding energies". Also other calculation tools, f.e. "Charge", "Protonation", "logP" and "Steric Hindrance" give different results.
The Marvin Huckel calculation tool is able to handle the pi-system of this dianion in correct D2h symmetry, both resonance formulas give the same result, see second screenshot bf0495.
What's wrong?
Regards, Hans-Ulrich