Question

Rank the following species in order of increasing basicity. Explain your reasons for ordering them as you do.

Short answer

A single structural formula sometimes cannot explain all the properties of a compound that is given. In such cases, the compound may be represented by two or more structural formulae which differ from each other only in the arrangement of electrons. None of this structural formula alone can explain all the observed properties of the compound. The compound is then said to show resonance. The various structures are known as resonating structures. The true structure of the molecule is not represented by any of the resonating structures but is considered to be a resonance hybrid of the various resonating structures.

Step-by-step solution

Resonance structures

A single structural formula sometimes cannot explain all the properties of a compound that is given. In such cases, the compound may be represented by two or more structural formulae which differ from each other only in the arrangement of electrons. None of this structural formula alone can explain all the observed properties of the compound. The compound is then said to show resonance. The various structures are known as resonating structures. The true structure of the molecule is not represented by any of the resonating structures but is considered to be a resonance hybrid of the various resonating structures.

Resonance effects on basicity

The basicity of common organic compounds is affected by resonance stabilization. Resonance delocalization of charges on a base helps in making the base more stabilized, and hence making it a weaker base and conjugate acid is strengthened.

Species in order of increasing basicity

Basicity mostly depends on electronegativity and delocalization of the negative charge of the base (anion). In anion (negatively charged ion) of sulfuric acid, the negative charge is delocalized on four highly electronegative oxygen atoms. So, will be the least basic. However, in amide the negative charge is not delocalized and it is present on the less electronegative nitrogen atom. So, is the most basic.