46 - Organic Chemistry

Question

Explain the observed difference in the $p{K}_a$  values of the conjugate acids of amines A and B.

Step-by-Step Solution

Answer

There is a difference between the $p{K}_a$ values of compound A and B because the lone pairs on N in compound A take part in the delocalization with the benzene ring. Thus, its basicity decreases, and it has a strong conjugate acid. 

Resonance

The movement of lone pairs or charges along in the conjugative system is termed resonance. It is also termed the delocalization of the pi electrons.

 

Explanation

In compound A, the lone pair on nitrogen is involved in the delocalization with the benzene ring. Due to this, the basicity of compound A decreases. Thus, it has stronger conjugate acid.

 

In compound B, the lone pair on nitrogen does not involve in the delocalization with the benzene ring as hindrance is created by the bridge atoms. Due to this, it is a stronger base. Thus, it has weaker conjugate acid.

 

Thus, there is a difference between the $p{K}_a$  values of compounds A and B.