Which of the following is the most acidic?

A $C X_{6} H X_{5} - OH$
B $CH X_{3} CH X_{2} - OH$
C $(CH X_{3}) X_{3} C - OH$
Dcyclohexanol

Answer: A

The phenoxide ion is stabilised by delocalisation of the negative charge into the ring, whereas alkoxide ions have localised charge destabilised by alkyl groups. Hence phenol (

p K_{a} \approx 10

) is far more acidic than alcohols (

p K_{a} \approx 16

18

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