Question

Among the following four compounds the acidity order is:
(a) Phenol

(b) methyl phenol
(c) meta nitrophenol

(d) para-nitrophenol

• A. $c>d>a>b$
• B. $a>d>c>b$
• C. $b>a>c>d$
• D. $d>c>a>b$

Answer 1

Answer: (D)

$d>c>a>b$

1. Para-nitrophenol(d) is more acidic because base abstract proton from OH group of phenol to form phenoxide ion is stabilized by nitro group present at Para position through resonance effect. Stability increase acidity also increases.
2. Meta-nitrophenol(c) is less acidic as compared to (d), because base abstract proton to form phenoxide is stabilized by electron-withdrawing inductive effect and this effect is less effective as compared to Resonance effect.
3. Phenol(a) is less acidic as compared (c)&(d), because No electron withdrawing group present on Phenol and resonance & inductive effect is absent here.
4. Methyl phenol shows the electrondonating Inductive effect that is donating group present on phenol as result destabilize phenol/ phenoxide, So it is least acidic

• Above discussion concluded that acidity order is as follows d>c>a>b
  

Option -D