How do you determine the pKa values of novel bases?

In summary, the conversation discusses the extraction of a product with a 50% yield and the separation of unwanted products. The importance of knowing the pKa values of the molecules is mentioned, and a method of selecting the right acid to form a salt of the wanted molecule is suggested. The question of determining the pKa value of a molecule with no experimental data is raised, and the possibility of using a program to analyze the structure and predict phase change temperatures is brought up. A link is provided for further information on determining pKa values.
  • #1
Zensation
12
0
Imagine there is a reaction performed and it contains a product that is easily separable via an acid base extraction. This product is only formed in 50% yield. The other 50% formed unwanted products that are to be separated and done away with.

If all that is known is the structure of these unknown molecules, how can they be extracted? I figure knowing the pKa values would be useful. Assuming the unwanted molecule is also soluble in the organic layer like the wanted molecule, and neither can be distilled out, the right acid could be selected to cause a salt to form of the wanted molecule but not the unwanted molecule.

My question is, how does one determine the pKa value off a molecule with no experimental data when only the structure is known? I can post pictures of the molecule shortly, but regardless of that, is there a way to determine pKa value off structure?

What would be really useful is if there was some sort of program that could analyze the structure of a molecule and determine when it is a solid/liquid/gas and the related temperatures of phase change. Anyone know of such a thing? I know Chemspider.com has a way to predict these values of molecules that are already in their database, but I have found no way to allow it to predict new molecules.
 
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  • #2
5 seconds googling, second link: http://www.uiowa.edu/~quantum/omtkypka.pdf
 
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1. What is the definition of pKa value?

The pKa value of a compound is a measure of its acidity, specifically the negative logarithm of the acid dissociation constant. It indicates the strength of an acid or base and how easily it can donate or accept a proton.

2. How do you measure the pKa values of novel bases?

The pKa values of novel bases can be determined through various methods such as potentiometric titration, UV-visible spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. These techniques involve measuring the change in pH or absorbance of the compound at different concentrations and using mathematical equations to calculate the pKa value.

3. Can pKa values be predicted for novel bases?

Yes, there are various computational methods available that can predict pKa values for novel bases. These methods use structural and electronic properties of the compound to estimate its acidity or basicity. However, experimental confirmation is still necessary for accurate determination of pKa values.

4. Are there any factors that can affect the accuracy of pKa values?

Yes, there are several factors that can affect the accuracy of pKa values. These include solvent effects, temperature, ionic strength, and impurities in the compound. It is important to control these factors during experiments to obtain reliable pKa values.

5. Why is it important to determine pKa values of novel bases?

Knowing the pKa values of novel bases is crucial for understanding their chemical and biological properties. It can help in predicting their reactivity, solubility, and potential medicinal uses. Additionally, pKa values can also aid in the design and synthesis of new compounds with desired properties.

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