Arrange the following compounds in order of increasing basicity (least to most)in aqueous solution:

Question

Quizplus · Accepted Answer

The basicity of an amine depends on the availability of the lone pair of electrons on the nitrogen atom. The more accessible the lone pair is, the more basic the compound. In this case, the compounds are:

I. CH3NH2
II. (CH3)2NH
III. (CH3)3N
IV. NH3

In order of increasing basicity, we need to consider the electronic effect of the substituents on the nitrogen atom. Compounds II and III are tertiary amines, which means they have three alkyl groups attached to the nitrogen atom. The high degree of steric hindrance makes the lone pair less accessible and decreases the basicity of these compounds. Therefore, II and III must be placed first and second in the order.

Compounds I and IV are primary and secondary amines, respectively, and have only one or two alkyl groups connected to the nitrogen atom. The basicity of a primary amine is greater than that of a secondary amine, which is greater than that of a tertiary amine. Therefore, compound IV is the most basic and should be placed at the end of the sequence. This leaves compound I as the third in line. Finally, we arrive at the following order of basicity:

II < I < III < IV

which corresponds to Choice (C).

Arrange the Following Compounds in Order of Increasing Basicity (Least