AIPMT – 1999

HINT:  Electron withdrawing group increases the acidity.

Explanation: 

Acidity of phenol / phenol derivatives depends on the stability of phenoxide ion. More the stability of phenoxide ion more is the acidity.

Electron releasing groups decreases the stability of conjugate base , decreasing it’s acidity.

Similarly, electron withdrawing groups increases the acidic nature by increasing the stability of conjugate base.

-NO₂ group increases the acidity of phenol. At p- position both -I effect and -M effect are present so it will be highly acidic. But at m- position only -I effect of -NO₂ will be there so m-nitro phenol is more acidic than phenol.

Due to -CH₃ group the acidity of  (A) will be least.

So correct order of acidity is  :  C > D > B > A

HINT: p-methyl diazonium chloride reacts with water to give p-cresol.

Explanation :

When aniline or it’s derivatives reacts with NaNO₂/HCl at very low temperature ($0^{0}C - 5^{0}C$) , then diazonium salts formation takes place.

Diazonium salts on reaction with water gives phenol / phenol derivatives. N₂ will be released during the reaction and -OH will replace $-N_{2}^{+}$ group.

So, p-methyl diazonium chloride reacts with water to give p-cresol.