Question

Arrange in increasing order of their acid strength giving reason: Propan-1-ol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol.

Answer 1

1. The order of increasing acidic character is :

Prop-1-ol < 4-Methylphenol < Phenol < 3-Nitrophenol < 3,5-Dinitrophenol

2. This is because,NO₂ group offers -I effect which pulls the electron density from H and easy to release H⁺.
Methyl group on the other hand increases electron density by +I effect thereby reducing the acidic character.
Prop-1-ol is aliphatic and does not stabilise O^- as efficiently as phenoxide ion via resonance.