Question

The correct order of reactivity of carboxylic acids towards esterification is

• A. HCOOH > CH3COOH > CH3CH2COOH > $\text{CH}_3\text{CH}(\text{CH}_3)\text{COOH}$ > $(\text{CH}_3)_3\text{C-COOH}$
• B. $(\text{CH}_3)_3\text{C-COOH}$ > $(\text{CH}_3)_2\text{CH - COOH}$ > CH3CH2COOH > CH3COOH > HCOOH
• C. CH3CH2CH2COOH > CH3CH2COOH > CH3COOH > HCOOH
• D. HCOOH > CH3CH2COOH > CH3COOH > $(\text{CH}_3)_3\text{C-COOH}$ > $(\text{CH}_3)_2\text{C-COOH}$

Answer 1

Answer: (A)

A. HCOOH > CH3COOH > CH3CH2COOH > $\text{CH}_3\text{CH}(\text{CH}_3)\text{COOH}$ > $(\text{CH}_3)_3\text{C-COOH}$

Answer 2

Esterification reactivity of carboxylic acids depends on the electrophilicity of the carbonyl carbon and steric hindrance. Electron-donating alkyl groups and steric bulk around the carbonyl carbon decrease reactivity. The order of increasing electron-donating strength and steric bulk is: H < CH$_3$ < CH$_3$CH$_2$ < (CH$_3$)$_2$CH < (CH$_3$)$_3$C. Consequently, the reactivity order of carboxylic acids decreases in the same sequence: HCOOH > CH$_3$COOH > CH$_3$CH$_2$COOH > (CH$_3$)$_2$CHCOOH > (CH$_3$)$_3$C-COOH.