Question

Arrange the following esters in the decreasing order of the rate of base hydrolysis.

• A. 1,2,3,4,5
• B. 5,3,5,2,1
• C. 1,2,3,5,4
• D. 5,4,3,2,1

Answer 1

The correct option is D 5,4,3,2,1

The correct order of base catalysed hydrolysis of esters are:

Rate of hydrolysis of ester is proportional to the ${\delta }^{+}$ charge on carbonyl carbon $(-\stackrel{O}{\stackrel{||}{\underset{{\delta }^{+}}{C}}}-)$.

The rate of hydrolysis for given compounds depends on the substituent present on the benzene ring.

Greater the $+R$ effect, smaller the magnitude of ${\delta }^{+}$ charge on the carbonyl carbon, smaller the electrophilicity of the carbonyl carbon and lesser the reactivity.

Greater the $-R$ effect, greater the magnitude of ${\delta }^{+}$ charge on the carbonyl carbon, greater the electrophilicity of the carbonyl carbon and greater the reactivity.

The groups $-OMe,-C{H}_3,-Cl$ have +R effect and decreases the electrophilicity of the carbonyl carbon.

The groups $-N{O}_2,-COC{H}_3$ have -R effect and increases the electrophilicity of the carbonyl carbon.

Order of $+R\text{effect}:-OMe>-C{H}_3>-Cl$
($-Cl$ also has -I effect)
Order of $-R\text{effect}:-N{O}_2>-COC{H}_3$

Hence, the reactivity follows the order,
$5>4>3>2>1$