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Question: The correct order of increasing basicity of given conjugate bases \(\left( {R = C{H_3}} \right)\) is...

The correct order of increasing basicity of given conjugate bases (R=CH3)\left( {R = C{H_3}} \right) is-
A.RCOO−<HC=C−<R−<NH2−{\text{RCO}}{{\text{O}}^ - } < HC = {C^ - } < {R^ - } < NH_2^ -
B.R−<HC=C−<RCOO−<NH2−{R^ - } < HC = {C^ - } < {\text{RCO}}{{\text{O}}^ - } < NH_2^ -
C.RCOO−<NH2−<HC=C−<R−{\text{RCO}}{{\text{O}}^ - } < NH_2^ - < HC = {C^ - } < {R^ - }
D.RCOO−<HC=C−<NH2−<R−{\text{RCO}}{{\text{O}}^ - } < HC = {C^ - } < NH_2^ - < {R^ - }

Explanation

Solution

Hint Basicity is determined by the number of hydrogen atoms replaced in the acid by a base. This means that the more readily the acid can donate protons, the more easily it can replace the proton by base. The molecule left after donating the proton is called the conjugate base of the acid.

Step-by-Step Solution
According to Bronsted- Lowry theory, the acid is proton donor and base is the proton acceptor. The acid after releasing the proton turns into a conjugate base. Here we have to determine the increasing basicity order of the given conjugate bases-
RCOO−{\text{RCO}}{{\text{O}}^ - } ,HC=C−HC = {C^ - }, R−{R^ - } and NH2−NH_2^ -
We know that the more the electrons are available, the more easily the molecule can donate protons and thus is a stronger base.
So in RCOO−{\text{RCO}}{{\text{O}}^ - } the negative charge is on oxygen after donating the proton which is an electronegative element so it will not share its electron pair easily. Hence it has the lowest basicity among the others.
R−{R^ - } has the highest basicity as the alkyl group is more readily available to donate the proton to form conjugate base and this conjugate base is more stable than the others.
Ammonia on donating a proton form conjugate base NH2−NH_2^ - which is strong base as compared to HC=C−HC = {C^ - } and RCOO−{\text{RCO}}{{\text{O}}^ - } as it does not have negative charge in electronegative element and is stable than these two. But it has less basic strength than the alkyl group.
HC=C−HC = {C^ - } is the conjugate base of alkene. It is more basic than RCOO−{\text{RCO}}{{\text{O}}^ - }as the electrons are more readily available to be donated.
So the order becomes-
RCOO−<HC=C−<NH2−<R−{\text{RCO}}{{\text{O}}^ - } < HC = {C^ - } < NH_2^ - < {R^ - }
Hence the correct answer is D.

Note: Many factors affect the basicity of a molecule they are-
1.Resonance- If the atom involved in the resonance has negative charge then the charge is delocalized which reduces the basicity. But if the atom involved in resonance does not have a negative charge then it does not affect the basicity of the molecule.
2.Atomic Radius- Atoms having a small radius will have more electron density than the atom having a large radius. Hence the smaller the atomic radius of the molecule the more the basicity.