question_answer

Which one of the following compounds is most acidic?                                     [AIPMT (S) 2005]

A) \[Cl-C{{H}_{2}}-C{{H}_{2}}-OH\]

B)

C)     

D)

Correct Answer: B

Solution :

[b] Phenols are much more acidic than alcohols, due to the stabilization of phenoxide ion resonance.

Phenoxide ion is stabilized due to following resonating structures:

While in alcohols

Ortho nitrophenol is most acidic because in it -NO2 electron attracting group is attached on ortho position which helps in stabilizing of negative charge on the oxygen of phenoxide ion Hence, due to this reason acidic character of phenol is increased, while on attachment of CH3 group (electron donating group) acidic strength of phenol is decreased in cresol due to destabihzation of phenoxide ion.