Question

Lower aliphatic amines are soluble in water. Why?

Hint:

Solubility of amines in water decreases as the size of the alkyl group increases due to increased hydrophobic character.

Answer 1

Step 1: Lower aliphatic amines contain the \(-\text{NH}_2\), \(-\text{NH}\), or \(-\text{N}\) group, which has a lone pair of electrons on nitrogen.
Step 2: This lone pair allows amine molecules to form hydrogen bonds with water molecules.
Step 3: In lower amines, the alkyl group is small, so the hydrophobic character is minimal and does not hinder solubility.
Step 4: As the size of the alkyl group increases, the hydrophobic effect increases and solubility decreases.