Question

Rank the compounds in each group in order of increasing basicity.

a.

b.

Short answer

a.

Order of basicity: $3>1>2$3>1>2

b.

Order of basicity: $1>2>3$

Step-by-step solution

Basicity

The basicity of a compound depends on the ease with which it can donate electrons.

Species that easily donate their electron pairs to others are termed as highly basic.

Factors affecting basicity

The presence of electron-withdrawing groups on a compound decreases its electron-donating tendency, thereby decreasing its basicity.

Order of basicity of the given compounds

a.

Compounds in a

In this, all the species consist of excess electrons that can be donated and all these are in conjugation with the phenyl ring.

Therefore, the basicity of the compounds can be determined by considering the electronegativity of the atoms that contain excess electrons.

Higher the electronegativity of the atom, lower will be its electron-donating ability, and hence lower will be its basicity.

The electronegativity of the elements is in the order: Oxygen>Nitrogen>Carbon

Therefore, the basicity of the compounds is in the order: $3>1>2$

b.

Compounds in b

The compound containing the electron-withdrawing nitro group is the least basic as the nitro group reduces the electron density on the oxygen atom.

The second compound is less acidic than the first as the electrons on its oxygen atom delocalizes over the ring, thereby decreasing its availability for donation.

Therefore, the basicity of the compounds is in the order: 1>2>3