Question

Among the following, the correct order of basicity is:
A) $N{H_2}^ - > O{H^ - } > R{O^ - } > RCO{O^ - }$
B) $N{H_2}^ - > R{O^ - } > O{H^ - } > RCO{O^ - }$
C) $RCO{O^ - } > N{H_2}^ - > R{O^ - } > O{H^ - }$
D) $RCO{O^ - } > R{O^ - } > N{H_2}^ - > O{H^ - }$

Answer 1

Hint: The basicity is the property of a molecule to accept hydrogen or a proton from another molecule. One can think about the structures which can accept a proton faster and decide the order.

Complete step by step answer:
1) First of all, the given structures of bases are all conjugate bases of acids.
2) So, we can relate the conjugate base strength based on the strength of their origin acids. The strong acids give the very weak conjugate base and the weak acids will give the strong conjugate base.
3) If we add a hydrogen atom in each base structure given then we will get the structure of their origin acids. We get the structure of origin acids as $N{H_3}$, ${H_2}O$, ${\text{ROH}}$, ${\text{RCOOH}}$.
4) The order of acidity of these structures from the strongest acid to weakest acid is $RCOOH > {H_2}O > ROH > N{H_3}$.
5) As the strong acid will give a weak conjugate base, the order of the conjugate base will be as, $N{H_2}^ - > R{O^ - } > O{H^ - } > RCO{O^ - }$ which shows that option B is the correct choice.
Thus option B is the correct answer.


Note:
As the strong acid readily donates a proton and forms anionic form of its conjugate base of that acid. As the conjugate base formed is due to the faster donation of proton it will not accept the proton easily as the base and hence it is a weak base. Also, the anion stability factor can determine the basicity of a structure. As nitrogen is less electronegative than oxygen, it will not stabilize the anion and hence readily accepts the proton to stabilize itself becoming more basic.