(a) Give the resonance structure of the conjugate bases of the following :

(b) Compare the stabilities of their bases and the acidites of the parent compounds.

Explanation

(a) (I)
(II)
(III)
(b) (I) Anion is stabilised due to aromaticity, althrough it has negative charge on less electronegative `C` atom.
(II) Anion is stabilished by `(p pi - p pi)` bond formation. It also has negative charge on less electronegative `C` atom but its anion is less stable than the anion of `(I)`.
(III) Anion is also stabilised by `(p pi - p pi)` bond formation, but the negative charge is delocalised to electronegative `O` atom, but some aromaticity of benzene is lost. So, anion is more stable than that of `(II)` but less stable than that of `(I)`
Therefore, stability order of the anions is :
`I gt III gt II`
The conjugate base is more stable if the negative charge is delocalised to more `EN` atom. Bit if an anion retains its aromaticity, it is even more stable.
The more stable the base (or weaker the base), the more acidic is the parent.
Acidic order is : `I gt III gt II`.