The compound shown is the parent phenol. Which of Structures A-D, each a derivative of it, is the strongest acid (the lowest $p K_{a}$ )?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: C

The parent compound is phenol (

p K_{a}

about 10). The 4-nitro compound is far stronger (about 7.2) because the nitro group delocalises the negative charge of the anion. 4-Methyl and 4-methoxy donate electrons and weaken the acid, and 4-chloro is only slightly stronger than phenol (about 9.4).

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The compound shown is the parent phenol. Which of Structures A-D, each a derivative of it, is the strongest acid (the lowest pKa​)?

Answer: C

More questions on Acidity and reactions of drawn phenols

The compound shown is the parent phenol. Which of Structures A-D, each a derivative of it, is the strongest acid (the lowest $p K_{a}$ )?