Question

The acid strength of active methylene group in given compounds decreases as
1. $C{H_3}COC{H _2}COO{C_5}{H_5}$
2.$C{H_3}COC{H_2}COC{H_3}$
3.${C_2}{H_5}OOCC{H_2}COO{C_5}{H _5}$
A. $a > b > c$
B. $c > a > b$
C. $a > c > b$
D. $b > a > c$

Answer 1

Hint: We can say inductive Effect is the phenomenon wherein a permanent dipole arises in a given molecule because of the unequal sharing of the bonding electrons in the molecule. This effect arises in sigma bonds. We have to know that there are two types of inductive effects. They are
1. Negative inductive effect or -I effect
2. Positive inductive effect +I effect

Complete step by step answer:
We can say when a chemical species with the affinity to release or donate electrons, like an alkyl group, is introduced to a carbon chain, the charge is relayed through the chain and the effect is called the Positive Inductive Effect or the +I Effect
We can say when an electronegative atom, like a halogen, is introduced to a chain of atoms (generally carbon atoms), the unequal sharing of electrons generates a positive charge that is transmitted through the chain. This causes a permanent dipole to arise in the molecule wherein the electronegative atom holds a negative charge and then we call it as a negative inductive effect. Negative inductive effect is otherwise known as electron withdrawing effect (or) –I effect.
Positive inductive effect in ester is more compared to ketone. Hence methylene anion will be more stable in case of ketone leading to more stable anion and more acidity.

Therefore, option (D) is correct .

Note:
We can also decide the acid strength in the active methylene group using the presence of electron withdrawing group and by the stability of the enolate anion obtained after ${H^ + }$ removal.
Higher the electron withdrawing ability of substituents bonded to electron withdrawing groups, higher would be acidic strength of methylene group. Electron withdrawing ability of $C{H_3}C{O^ - }$ is greater.