When your body metabolizes amino acids, one of the final end products is urea, a water so liable compound that is removed from the body as urine. Why is urea soluble in water, when hexamide, a related compound is not?

To understand why urea is soluble in water while hexamide is not, we need to consider the molecular structure and intermolecular forces involved.

Urea (CH4N2O) and hexamide (C6H12N2O) both contain the amide functional group (-CONH2), which consists of a carbonyl group (C=O) connected to an NH2 group. However, hexamide has a longer carbon chain compared to urea.

The solubility of a compound in water is determined by the intermolecular forces acting between the compound and water molecules. In the case of urea, it is highly soluble in water due to hydrogen bonding interactions.

Urea has two hydrogen bonding sites: one at the oxygen atom of the carbonyl group and the other at the nitrogen atom of the amino group. Water molecules (H2O) can form hydrogen bonds with these sites, leading to the dissolution of urea in water.

In contrast, hexamide has a longer carbon chain, which makes it less soluble in water. The longer carbon chain does not have a highly polar functional group (like the carbonyl and amino groups in urea), which can participate in extensive hydrogen bonding interactions with water molecules. Consequently, the intermolecular forces between hexamide and water are weaker, resulting in poor solubility.

In summary, urea's solubility in water is due to its ability to form hydrogen bonds with water molecules, while hexamide's lack of solubility is primarily attributed to its longer carbon chain, which reduces its ability to form strong hydrogen bonds with water.