What is the relationship between tautomers and pka in terms of pH?

[RedVelvetCake]

in terms of pka and tautomers
if a base has a pka of 3.8
with a ph below and above the pka would the amino or imino group predominate
and with a ph above and below the pka would a keto or enol predominate. I am a little confused figuring them out
Nikki

 

[chem_tr]

First, a base should have a pK_a much higher than 3.8; this better fits an acid like acetic acid whose pK_a is around 4.7. If you are above the pK_a value, you can expect it to be deprotonated like A; below pK_a it is surely protonated as in HA.

I presume that keto-enol or amino-imino tautomerism has nothing to do with pK_a much. We sometimes need a special tautomer to explain the reaction types as in mechanisms.

 

[movies]

I assume that you mean imino-enamine tautomers. Amines and imines are more like alcohols and ketones.

 

[sinemcik]

:(.....