Wrong ascorbate ion (Vitamin C)

Hi,

calculating the pKa-values and the mono-anion of ascorbic acid (vitamin C) there is a wrong structure for the mono-anion, see attached image. And the two first pKa-values are shown at wrong OH positions.

The first deprotonation occurs at the vinylogous carbonic acid and not at the OH-group in the middle. The mono-anion is resonance stabilized (mesomerism).

The di-anion is correct.

For the experimental values I found: pKa1 = 4.2 and pKa2 = 11.6.

I have also attached the pubchem description. There one can find the SMILES code for the sodium salt with the anion in position 3: C([C@@H](C1C(=C(C(=O)O1)O)[O-])O).[Na+]

Regards, Hans-Ulrich

Hi,

Yes , the " pKa  -  assigned atom " couple is not correct in this case. I try to fix this problem asap. 

Jozsi

Hi Jozsi,

this evening time you are sending me this answer, is realy remarkable !   Thank you !

Vitamin C is an important molecule. Pauling was a fan of it.

Best regards, Hans-Ulrich

Good Morning Hans!

 

This fix will appear in the 5.3.3 version.

 

Jozsi