Question

Which of the following is the strongest base in aqueous solution ?

• A. Methylamine
• B. Trimethylamine
• C. Aniline
• D. Dimethylamine

Answer 1

Answer: (D)

Note : Aromatic amines are less basic than aliphatic amines. Among aliphatic amines the order of basicity is $2^{\circ }>1^{\circ }>3^{\circ }$. The electron density is decreased in 3° amine due to crowding of alkyl group over N atom which makes the approach and bonding by a proton relatively difficult. Therefore the basicity decreases. Further Phenyl group show - I effect, thus decreases the electron density on nitrogen atom and hence the basicity.
$\therefore$ Dimethylamine ($2^{\circ }$ aliphatic amine) is strongest base among given choices.
$\therefore$ The correct order of basic strength is
Dimethylamine > Methyl amine > Trimethyl amine > Aniline.PRACT