Question

Which of the following species can act as the strongest base?

• A.
• B. $R{O}^{-}$
• C. $H{O}^{-}$
• D. $C_6{H}_5{O}^{-}$

Answer 1

The correct option is D $C_6{H}_5{O}^{-}$

$\text{Comparing the basic strengths of the given anions}:$

Strength of bases is related to the ease of accepting a proton which in this case depends on the availability of electron pair on oxygen. More is the availability of electron pair, more easily the proton will be accepted and more will be the basic strength.


In compounds $\left(C\right)$ and $\left(D\right)$ negative charge on oxygen will be delocalised on benzene ring so it will be less available to accept proton.



Moreover, compound $\left(D\right)$ will be less basic than $\left(C\right)$ because of $-I$ and $-M$ effect of $-N{O}_2$ group which further decreases the electron density.

Compound $\left(B\right)$ will be more basic than $\left(A\right)$ because of the positive inductive effect of the alkyl group which increases the electron density on oxygen atom.


So, order of electron density among given compounds will be:

$\left(B\right)>\left(A\right)>\left(C\right)>\left(D\right)$

Hence, compound $\left(B\right)$ will be the strongest base
So, the correct answer is option $\left(B\right)$.