Arrange the following compounds in the increasing order of their acidic strength :
i. m - nitrophenol ii. m - cresol
iii. Phenol iv. m -chlorophenol

Options

A. `ii lt iv lt iii lt i`
B. `ii lt iii lt i lt iv `
C. `iii lt ii lt i lt iv`
D. `ii lt iii lt iv lt i`

Answer

D

Explanation

Nitro group has both - R effect and - I effect , but - R effect predominates . Due to stronger electron with drawing nature of - `NO_(2)` group , phenoxide ion is stabilized more . Hence nitrophenol is more acidic than phenol .
Methyl group destabilizes the phenoxide ion by + I effect and hyperconjugation . Hence m - cresol is weaker acid than phenol . - R effect of nitro group is stronger than - I effect of chlorine , hence m - nitrophenol is more acidic than m - childphenol .
Therefore the correct order of acidic strength is m - nitrophenol `gt` m - chlorophenol `gt` phenol `gt ` .