Question

Which of the following is correct for stability of phenoxide ion?
A.Resonating structure of benzene ring
B.Localization of $\pi$ electrons in phenoxide ion
C.Delocalization of $\pi$ electrons in phenoxide ion
D.All of the above

Answer 1

Phenols are compounds having a hydroxyl group attached to a benzene ring. They are acidic compounds and known as carbolic acids due to the stability of the conjugate base so formed, phenoxide ion.

Complete step by step solution:
Phenols are acidic and thus lose a proton, ${{\text{H}}^ + }$ from the hydroxyl group forming a phenoxide ion. The oxygen atom in phenoxide ion is highly electronegative and thus has high electron density.
In the phenoxide ion structure, the oxygen atom is connected to an $s{p^2}$ carbon atom which has a high electronegativity. It helps stabilize the negative charge on the oxygen atom to some extent. The negative charge on the oxygen atom is distributed along the benzene ring through the delocalization of $\pi$ electrons in the benzene ring. This provides extra stability to the phenoxide ion.

Thus, the correct option is C.

Note: The stability of the phenoxide ion is also affected by the substituent groups present on the benzene ring. If an electron donating group is present as a substituent on the phenoxide ion, it pushes the electron density towards an already negative oxygen atom carrying high charge density. This reduces the stability of phenoxide ions. If an electron withdrawing group is present as a substituent on the phenoxide ion, it pulls the electron density away from the negative oxygen atom carrying a high charge density. This reduces the negative charge density on the oxygen atom providing extra stability to the phenoxide ion. Also the presence of substituent at the ortho and para positions affects the stability of phenoxide ion more significantly as it withdraws or donates electrons through mesomeric effect.