Question

Ionic species are stabilized by the dispersal of charge. Which of the following carboxylate ion is the most stable?

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Factors affecting the stability of carboxylate ion :

Carboxylate ions are stabilised by the dispersal of negative charge. Electron withdrawing group decreases the negative charge density thereby increases the stability of carboxylate ion.

Analysing the given options

Option $\left(A\right)$:




No electron withdrawing groups are attached at neighbouring position of carboxylate ion. So, extra stabilisation of carboxylate ion doesn’t occur due to absence of electron withdrawing groups.

Option $\left(B\right):$

Chlorine atom is attached at neighbouring position of carboxylate ion, which can act as electron withdrawing group due to it’s $-I$ effect.

So, extra stabilisation of carboxylate ion occurs due to presence of electron withdrawing group. Hence, it is more stable than option $\left(A\right).$

Option $\left(C\right):$

Fluorine atom is attached at neighbouring position of carboxylate ion, which can act as electron withdrawing group due to it’s $-I$ effect.

Since, fluorine is more electronegative than chlorine. So, it will exert stronger $-I$ effect than chlorine. Hence, it will have more stabilisation of carboxylate ion than option $\left(B\right).$

Option $\left(D\right):$



$2$ Fluorine atoms are attached at neighbouring position of carboxylate ion, which can act as electron withdrawing groups due to their $-I$ effect.

Since, two fluorine atoms will exert stronger $-I$ effect than single fluorine. Hence, it will have most stabilisation of carboxylate ion.

So, correct answer is option $\left(D\right)$