Correct order of pKa values:

Question

Canvas Classes · Accepted Answer

Step 1: Acidic Strength () and Electronic Effects
. Lower  means stronger acid.
- (iii) p-nitrophenol: Strong  and  from nitro group makes it the strongest acid (lowest ).
- (i) Phenol: Reference.
- (iv) p-tert-butylphenol:  from tert-butyl group slightly decreases acidity.
- (ii) p-dimethylaminophenol: Strong  from  significantly decreases acidity (highest ).

Step 2:  Order (Weakest acid to Strongest acid)
(ii)  (iv)  (i)  (iii).

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