Acetic acid, pKa. A big mistake

Marvin 5.6.0.1

Hi,

The problem with the calculation of acid-base properties of acetic acid ...
1) Calculation = 4.54?
Literature = 4.76
2) Do not calculate the protonation constant of the carboxyl (must bedigit blue)

Sorry,

AlexandrI

Hi,

I think  that the difference between the experimental and the predicted pKa values is not too large. It is reasonable.

Your (2nd) comment is not clear for me.  

Jozsi

Hi,

With our pKa calculator only the "pKa"  values are calculated either  the "red or blue text font"  colors are used for displaying  of  the numerical values on the screen.

The "pKb" values of molecules are not calculated at all ,nowhere with our pKa calculator.

Under the default settings the "colors" will have  the next simple attribute:

The red color means that the molecule is acidic in its neutral state. (e.g. acetic acid)

The blue color means that the molecule is basic in its neutral state. (e.g. aliphatic amin)

Don't worry about your English ,it is OK.

Jozsi

Hello Jozsi,
Thank you for your reply.
I realized that the acetic acid - a bad model for my interests.
Please consider a specific well-studied experimentally by me cationic form of the dye. Before asking about the meaning of numbers - I shock asymmetry pKa. Because the structure is symmetric and quantum-chemical calculations indicate the symmetry of its ...

AleksandrI

Hi,

There are two identical intrinsic pKa couples due to symmetry  in your molecule. See the attached figure from your molecule. 

Jozsi

[Marvin 5.6.0.2, Calculator]

Hi,

I understood:
1. If you do MICRO, then there is only one structure with a symmetrical arrangement of the correct pKa (your file).
2. If you do MACRO, then there is a structure with an asymmetric arrangement of pKa, which is wrong. But in this case is a diagram of distribution of microparticles (my file).
3. If this the diagram corresponds to an incorrect figure with incorrect placement of pKa, then the diagram itself is wrong!
Logical?
Р. S.  I watched the entire our Forum on the words MICRO CONSTANTS and found a complete fog of ivagueness ...

AlexandrI

Hi,

2. If you do MACRO, then there is a structure with an asymmetric arrangement of pKa, which is wrong.  

This molecule has 4 different macro pKa values. Their symmetric arrangement is not possible since they are different,therefore,this figure is justified. 

Not clear for me what  you mean on "wrong".

 Jozsi

Hi,  Jozsi !

I have performed two calculations: in macro mode (the attached file1MAKRO.png) and in micro mode (attached file 1MIKRO.mol).
Why digits are different?

 What pKa suitable for use in predicting the order of the ionization of the molecule?

AlexanderI

P.S. Why possible to attach only one file? (1MIKRO - no)

Hi,

You can create analytical expression for calculating of the "Macrco Ka" values. All of  the "Macro Ka" values are can be expressed as function of the "micro ka" values. Ka=f(ka1,ka2,ka3,..kan)

For example the first ionization constant "Ka1" is algebraic sum of  the "micro ka" values:   

Ka1=ka1+ka2+ka3+ka4

The second "Ka2" ,the third "Ka3" and the forth "Ka4" macro ionization constants have more complicated dependency on the "micro ka" values.

The "Macro Ka"  is the  experimentally available ionization constant "Ka".

Micrsospecies distribution at given pH value can be calculated from the "micro ka" values.

Macrospecies distribution can be calculated at given pH from the "macro Ka" values.  

 

Why possible to attach only one file? (1MIKRO - no) 

 

I'm going to ask info from  this about our site moderator. I don't have this problem under Windows XP operation system. 

 Jozsi

Hi, Jozsi

 

Unfortunately, your final answer hung in the air.
This should be the answer to my question about how to useMarvin to obtain numerical values ​​microconstants.
But my question has disappeared from the Forum and should bein front of your answer. If I did not send it, you would not answer!
Please help find my last post for which you have given the last post, so I could comment on it!
I'm waiting for some time, and then repeat the question. So in your post I have not found answers to my main question: how to useMarvin to obtain numerical values ​​microconstants?
 

Alexander

Hi,

In your previous answer you wrote:

I have performed two calculations in macro mode (the attached file1MAKRO.png) and in micro mode (attached file 1MIKRO.mol).

So you can use Marvin, because micro and macro calculation was done by you.

Here is your other forum topic what was opened by you on   Sun Oct 16, 2011 6:41 am 

https://www.chemaxon.com/forum/viewtopic.php?p=37858

 

Jozsi

Hi,

By the way:

 If I did not send it, you would not answer!

No,no. I just respond for your "MACRO pKa" calculation you were able to attached above , and you were suprised why the maco pKa values are different.

Jozsi

Hi Alexander,

AlexandrI wrote:

P.S. Why possible to attach only one file? (1MIKRO - no)

As far as I can see, you can upload multiple files. Make sure you click on the "Add attachment" button after choosing the first file, this will store the first file, reload the page and give you a second box for an second attachment.

Cheers,
Andras