Amino acids have high boiling point because

A. of the formation of Zwitter ion

B. of dipolar nature.

C. of strong dipole-dipole interaction

D. of strong intermolecular forces

E. of the presence of \(-COOH\) and \(-NH_2\) at \(\alpha \)-position

Choose the correct answer from the options given below:

A, B, C, D only

The correct answer is option 3. A, B, C, D only.

Amino acids are organic molecules that contain both an amino group \((-NH_2)\) and a carboxyl group \((-COOH)\). They also have a side chain (R group) attached to a central carbon atom, known as the alpha carbon. This structure gives amino acids their characteristic properties, including their ability to form strong intermolecular interactions, which contribute to their high boiling points.

Here is a breakdown of the factors contributing to the high boiling point of amino acids:

A. Formation of Zwitterions : In the solid state, amino acids exist predominantly in the form of zwitterions. In this form, the amino group donates a proton to the carboxyl group, resulting in the formation of an internal salt. This zwitterionic structure enhances the intermolecular interactions between amino acid molecules, leading to a higher boiling point.

B. Dipolar Nature: Amino acids are dipolar molecules because they contain both acidic \((-COOH)\) and basic \((-NH_2)\) functional groups. This dipolarity results in a separation of charge within the molecule, with the amino group carrying a positive charge and the carboxyl group carrying a negative charge. As a result, amino acids can form strong dipole-dipole interactions with neighboring molecules, which increases their boiling points.

C. Strong Intermolecular Forces: The presence of polar functional groups (\(-COOH\) and \(-NH_2\)) in amino acids leads to strong intermolecular forces such as hydrogen bonding and dipole-dipole interactions. Hydrogen bonding, in particular, is a significant contributor to the high boiling point of amino acids. Hydrogen bonds form between the hydrogen atom of one amino acid molecule and the electronegative atom (usually oxygen or nitrogen) of another molecule. These bonds are relatively strong and require a significant amount of energy to break, thus raising the boiling point of amino acids.

D. Strong dipole-dipole interaction: Strong dipole-dipole interactions are indeed one of the key factors contributing to the high boiling point of amino acids.

Amino acids contain functional groups such as the amino group \((-NH_2)\) and the carboxyl group \((-COOH)\), both of which are polar in nature. Due to differences in electronegativity between the atoms within these functional groups, they exhibit permanent dipole moments.

When amino acids are in the liquid or solid state, these polar functional groups align themselves in a way that maximizes the attractive forces between molecules. As a result, amino acids can form strong dipole-dipole interactions with neighboring molecules.

These dipole-dipole interactions contribute significantly to the cohesive forces between amino acid molecules. They require a considerable amount of energy to overcome, which results in a higher boiling point for amino acids compared to non-polar compounds of similar molecular weight.

Therefore, strong dipole-dipole interactions play a crucial role in determining the physical properties of amino acids, including their high boiling points.

E. Presence of \(-COOH\) and \(-NH_2\) at Alpha Position:  The statement "Amino acids have high boiling point because of the presence of \(-COOH\) and \(-NH_2\) at the alpha position" is partially incorrect. While these functional groups are present and influence boiling points, it's their combined effect that's crucial.

Here's why the statement needs clarification:

\(-COOH\) and \(-NH_2\) groups are present: This part is true. Amino acids do have a carboxylic acid group \((-COOH)\) and an amino group \((-NH_2)\) in their structure.

Alpha position: This is also true. These groups are typically located on the same carbon atom (the alpha carbon) in most proteinogenic amino acids.

However, the statement focuses solely on the presence of these groups at a specific location. The high boiling point arises due to the interactions between these functional groups.

In summary, the high boiling point of amino acids is a result of the combined effects of their zwitterionic nature, dipolar character, strong intermolecular forces, and the specific arrangement of functional groups at the alpha position. These factors make amino acids important building blocks of proteins and significant contributors to various biological and chemical processes.