Consider the following order of acidity based on pKa values:-
ethanoic acid > phthalimide >phenol >water >acetamide
Looking towards similar questions on stack exchange such as this , the recurring theme is that both quality(the electronegativities of the atoms on which charge is delocalized)as well as quantity of resonance(the number of resonating structures) should be seen when determining the stability of conjugate base and quality is given precedence over quantity. However, this doesn't seem to work here. Let me categorize the conjugate bases of the aforementioned compounds:-
- Ethanoic Acid- Delocalisation over 2 oxygen atoms
- Phtalimide- Delocalisation over 2 oxygen atoms and 1 nitrogen atom
- Phenol-Delocalisation over 1 oxygen atom and 3 carbon atoms
- Water-Localised over 1 oxygen atom
- Acetamide- Delocalisation over 1 oxygen atom and 1 nitrogen atom
Now, based on the linked question, we get ethanoic acid > phenol > water where we have seen quality of resonance first then quantity. However, this doesn't work for phtalimide which should be placed above carboxylic acid and also acetamide which should be placed above water and possibly even phenol.
So how would you explain this order?