COMEDK2015ChemistryCarboxylic Acid Derivatives
Consider the acid strength of the carboxylic acids. ~ I . ~ P h C O O H ~ I I . ~ o - N III. p- NO ₂ C ₆ H ₄ COOH IV. m- NO ₂ C ₆ H ₄ COOH
Options
- AI > II > III > IV
- BIV >I I I>I I>I
- CII >I I I>I V>I
- DII >I V>I I I>I
Correct answer
C. II >I I I>I V>I
Step-by-step solution
Due to -I and -R -effects of - NO ₂ group, nitrobenzoic acids are stronger acids, than benzoic acid Due to ortho-effect, o -nitrobenzoic acid is the strongest acid. In p -nitrobenzoic acid both -R -effect and -I -effect of the - NO ₂ group increase the acidity, while in m -nitrobenzoic acid only the weaker -I -effect increases the acidity. Hence, the order of acidic strength is o -nitrobenzoic acid >p -nitrobenzoic acid >m -nitrobenzoic acid > benzoic acid.