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JEE Main levelSingle correct optionDifficulty 2 of 3g2254

Which hydrogen of the compound shown is the most acidic?

Aboth X-H hydrogens are equally acidic
Bthe O-H hydrogen
Cthe ring hydrogens ortho to the SH
Dthe S-H hydrogen

Answer: D

The compound is 4-mercaptophenol. Thiols are more acidic than the corresponding alcohols and phenols: aromatic S-H has pKa about 6.5 (thiophenol 6.6), phenolic O-H about 10. The larger sulfur atom stabilises the negative charge better.

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