Problem 141 - A Complete Resource Book in Chemistry for JEE Main

Question

A substance forms zwitter ion. It can have functional groups (a) \(-\mathrm{NH}_{2},-\mathrm{COOH}\) (b) \(-\mathrm{NH}_{2},-\mathrm{SO}_{3} \mathrm{H}\) (c) both (d) none of these

Step-by-Step Solution

Answer

Both (a) and (b) can form zwitter ions, so the answer is (c) both.

Step 1: Understanding Zwitter Ions

A zwitter ion is a molecule that contains both positive and negative charges, but is overall neutral. It typically occurs when a molecule has both an acidic group and a basic group. The classic example of a zwitter ion is an amino acid, in which the acidic carboxylic group (-COOH) and the basic amino group (-NH2) can simultaneously deprotonate and protonate respectively.

Step 2: Identify Functional Groups

Review the given functional groups: (a) -NH2 and -COOH, (b) -NH2 and -SO3H. Both -COOH and -SO3H are acidic groups capable of donating a proton, while -NH2 is a basic group capable of accepting a proton.

Step 3: Analyzing Option A

For option (a) -NH2 and -COOH, the -COOH can donate a proton to form -COO-, and the -NH2 can accept a proton to form -NH3+. This means option (a) can form a zwitter ion.

Step 4: Analyzing Option B

For option (b) -NH2 and -SO3H, the -SO3H can donate a proton forming -SO3-, and the -NH2 can accept a proton to form -NH3+. This means option (b) can also form a zwitter ion.

Step 5: Conclusion

Both options (a) and (b) can form zwitter ions due to the presence of suitable acidic and basic groups. Hence, the correct answer is (c) both.

Key Concepts

Acidic and Basic Functional Groups

Functional groups play a crucial role in determining the chemical behavior of molecules, particularly in organic chemistry. When we talk about acidic and basic functional groups, we are referring to groups that can either donate or accept protons (H+ ions).

• Acidic functional groups, such as carboxylic acids (-COOH), are capable of donating a proton. This results in the formation of a negatively charged group, like the carboxylate ion (-COO-).
• Basic functional groups, on the other hand, like the amine group (-NH2), can accept a proton, turning into a positively charged group (-NH3+).
• Sulfonic acids (-SO3H) are also examples of strong acidic groups that can easily donate a proton to form a sulfonate ion (-SO3-).

The interplay between these functional groups is what allows complex molecules such as zwitter ions to form, as they balance each other out to create a molecule that is electrically neutral yet contains distinct charges.

Amino Acids

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid has a basic structure that includes:

• An amino group (-NH2), which is basic and can accept a proton.
• A carboxylic acid group (-COOH), giving it acidic properties.
• An organic "R" group, providing unique properties to each amino acid.

Prototypical amino acids like glycine can form zwitter ions, where the amino group accepts a proton and the carboxylic acid donates it. This dual capability of amino acids to contain both an acidic and basic component is pivotal in biological systems, affecting protein structure and function. For instance, the zwitterionic form of amino acids is vital for the solubility of proteins in water and their interactions with other biomolecules.

Protonation and Deprotonation

Protonation and deprotonation are chemical processes involving the gain or loss of a hydrogen ion, respectively.

• Protonation refers to the addition of a proton (H+) to a molecule, turning a basic functional group like -NH2 into -NH3+.
• Deprotonation, in contrast, involves the removal of a proton from an acidic group, such as the transformation of -COOH into -COO-.

These reactions are fundamental to acid-base chemistry and occur in numerous biological and chemical systems. In the context of zwitter ions, these processes happen simultaneously, facilitating the existence of a molecule that has both positive and negative charges. This balance is instrumental in mediating interactions in biochemical pathways and stabilization of molecular structures.