Ranking bases vs acids on the DAT (which is more common?)

[510586]

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I noticed during Chad's ochem videos that he ranks bases first then ranks conjugate bases to rank acids. Why is this? On the DAT, do they ask for basicity of compounds when comparing them more often than acids? Not a very important question, just curious. Seems like ranking acids is more practical since you can just say more stable (after plus charge) means more acidic.

 

[DAT Destroyer]

I noticed during Chad's ochem videos that he ranks bases first then ranks conjugate bases to rank acids. Why is this? On the DAT, do they ask for basicity of compounds when comparing them more often than acids? Not a very important question, just curious. Seems like ranking acids is more practical since you can just say more stable (after plus charge) means more acidic.

You should have an idea about pKa values for acidity. For example.... carboxy acids are about 5..as well as aromatic ammonium ions.. phenol is 10.......alcohols are about 16......aldehydes and ketones around 17. Amines around 35....alkenes around 44...and alkanes around 50. a protonated alcohol is around NEGATIVE 2 !!!!! Also understand that the more stabilized an anion is.....the more acidic the compound. For example, carboxy acids are more stable than alcohols, Why ?

EXAMINE THE ANION.....the anion has resonance to delocalize the negative charge,,,this is not seen in the anion of the alcohol. For bases.....start with the understanding that amines are generally bases...with AROMATIC amines less basic since the benzene ring withdraws electron density away from the N and prevents it from capturing a proton. Amines like Pyrrole are HORRIBLE bases since they are aromatic !!! Protonation would disrupt the aromaticity.

Now for the tricky part....

As a rule.... if in the gas phase.....tertiary amines are the most basic.......in aqueous solutions secondary amines are most basic. I recommend you get a good organic text and glance at what I have written here.

I have read virtually every book in Organic Chemistry, and can refer you to easy to read books by Klein, Carey, Wade, Jones, McMurray, Bruice, Smith, Solomons ,Browne and Foote... who have explained this in easy language. Once you think you understand the concepts.....try a few problems relating acidity and basicity trends.... BOTH are important.

Hope this helps.

Dr. Jim Romano

 

[510586]

You should have an idea about pKa values for acidity. For example.... carboxy acids are about 5..as well as aromatic ammonium ions.. phenol is 10.......alcohols are about 16......aldehydes and ketones around 17. Amines around 35....alkenes around 44...and alkanes around 50. a protonated alcohol is around NEGATIVE 2 !!!!! Also understand that the more stabilized an anion is.....the more acidic the compound. For example, carboxy acids are more stable than alcohols, Why ?

EXAMINE THE ANION.....the anion has resonance to delocalize the negative charge,,,this is not seen in the anion of the alcohol. For bases.....start with the understanding that amines are generally bases...with AROMATIC amines less basic since the benzene ring withdraws electron density away from the N and prevents it from capturing a proton. Amines like Pyrrole are HORRIBLE bases since they are aromatic !!! Protonation would disrupt the aromaticity.

Now for the tricky part....

As a rule.... if in the gas phase.....tertiary amines are the most basic.......in aqueous solutions secondary amines are most basic. I recommend you get a good organic text and glance at what I have written here.

I have read virtually every book in Organic Chemistry, and can refer you to easy to read books by Klein, Carey, Wade, Jones, McMurray, Bruice, Smith, Solomons ,Browne and Foote... who have explained this in easy language. Once you think you understand the concepts.....try a few problems relating acidity and basicity trends.... BOTH are important.

Hope this helps.

Dr. Jim Romano

Thank you! I will refer back to this post in the future when doing these types of problems if I ever get confused.

 

[DAT Destroyer]

Thank you! I will refer back to this post in the future when doing these types of problems if I ever get confused.

Glad I could help out!🙂