Question

Which has the highest $p{K}_b$ value ?

• A. $R_{3}N$
• B. $R_{2}NH$
• C. $RN{H}_2$
• D. $N{H}_3$

Answer 1

The correct option is D $N{H}_3$

Ammonia is a weak base so it has pK value of 4. So the order of basicity is ammonia<primary<tertiary amines <secondary amines. This order depends on steric hindrance. The size of alkyl group is more than that of hydrogen atom. So alkyl group hinders the attack of hydrogen atom and decreases the basicity of molecule. So more the number of alkyl groups lesser will be its basicity.