Consider the type of orbitals involved, and rank the following nitrogen compounds in order of decreasing basicity. Give the structure of their conjugate acids; and estimate their pK_as from similar compounds in Appendix 4. Rank the conjugate acids in order of increasing acidity. (Hint: These two orders should be the same!)

The residual part of acid after losing a proton (H⁺) will have a tendency to accept a proton (H⁺) . Therefore, it will behave as a base. These pairs of substances which differ from one another by a proton (H⁺) are known as conjugate acid-base pairs. Consider a general example of an acid:

K_a is known as the acid dissociation constant and its value indicates the relative strength of the acid. pK_a is defined as the negative logarithm (base 10 ) of K_a. Mathematically, pK_a= -logK_a. pK_a value of strong acids is usually zero or even negative while the pK_a value of weaker acids are greater than 4.

The mixing of atomic orbitals to give equal number of symmetrically hybridized orbitals is known as hybridization. The different types of hybridization are sp , sp² , sp³ , sp³d, sp³d² or d²sp³, sp³d³. sp hybridization is linear with a bond angle of 180⁰, sp² hybridization is trigonal planar with a bond angle of 120⁰and sp³ hybridization is tetrahedral with a bond angle of 109.5⁰.

Acidity of N-H bonds vary with hybridization in the order sp>sp²>sp³ which means that basicity will decrease in the order sp³>sp²>sp.