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

Question

A substance forms zwitter ion. It can have functional groups [2002] (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

Option (c) both.

Step 1: Understanding Zwitterions

A zwitterion is a molecule that contains both a positive and a negative charge but is overall neutral. It typically forms when a compound contains both an acidic and a basic functional group.

Step 2: Identifying Functional Groups

We need to identify the functional groups in the given options: - Option (a) has amino group \(-\mathrm{NH}_2\) which is basic and carboxyl group \(-\mathrm{COOH}\) which is acidic. - Option (b) has amino group \(-\mathrm{NH}_2\) and sulfonic group \(-\mathrm{SO}_3\mathrm{H}\), which is also acidic.

Step 3: Analyzing Option (a)

For the \(-\mathrm{NH}_2\) and \(-\mathrm{COOH}\) pair, the \(-\mathrm{NH}_2\) can accept a proton to become \(-\mathrm{NH}_3^+\) and the \(-\mathrm{COOH}\) group can lose a proton to become \(-\mathrm{COO}^-\), forming a zwitterion.

Step 4: Analyzing Option (b)

For the \(-\mathrm{NH}_2\) and \(-\mathrm{SO}_3\mathrm{H}\) pair, the \(-\mathrm{NH}_2\) can accept a proton to form \(-\mathrm{NH}_3^+\) and the sulfonic group \(-\mathrm{SO}_3\mathrm{H}\) can lose a proton to form \(-\mathrm{SO}_3^-\), also forming a zwitterion.

Step 5: Conclusion

Both Option (a) and Option (b) have the potential to form zwitterions because both contain one functional group that can become positively charged and another that can become negatively charged at the same time.

Key Concepts

Functional groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. These groups play a critical role in determining the properties and reactivity of organic compounds.
For instance, functional groups can make a molecule acidic, basic, or neutral. They can also affect the molecule's solubility in water or its ability to form bonds with other molecules. A single molecule can have multiple functional groups, and this variety can contribute to its overall behavior. In the exercise above, we discuss three types of functional groups that facilitate the formation of a zwitterion: amino, carboxyl, and sulfonic groups.
Understanding functional groups is essential for anyone studying chemistry, as it allows a prediction of how different substances will react with each other. It also forms the foundation for more advanced topics in organic chemistry.

Amino group

The amino group, represented as \(-\mathrm{NH}_{2}\), is one of the essential functional groups in chemistry. It contains a nitrogen atom bonded to two hydrogen atoms and can act as a base.

Properties of Amino Group

- Because of the lone pair of electrons on the nitrogen atom, the amino group can attract and accept a proton (H\(^+\)), making it positively charged.- It is commonly found in amines and amino acids, which are vital in biological processes.The ability of the amino group to accept a proton is critical in the formation of zwitterions. In amino acids like glycine, the amino group becomes \(-\mathrm{NH}_3^+\) by accepting a proton, playing an integral role in its zwitterionic structure. The nature of the amino group as a base contributes to its widespread presence in organic molecules.

Carboxyl group

The carboxyl group, denoted as \(-\mathrm{COOH}\), is a functional group that is both prominent and significant in organic chemistry. It consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (OH). This configuration allows it to donate a proton (H\(^+\)), characterizing it as an acid.

Characteristics of the Carboxyl Group

- The carboxyl group can lose a hydrogen ion to form \(-\mathrm{COO}^-\), making it negatively charged.- It plays a crucial role in the structure of amino acids, fats, and other biological molecules.This group's ability to donate a proton is essential for zwitterion formation. In the exercise, the carboxyl group becomes \(-\mathrm{COO}^-\) when it loses a proton, balancing the positive charge from the amino group's gained proton. The carboxyl group's acid nature gives molecules the potential to behave as weak acids in solutions.

Sulfonic group

The sulfonic group, represented by \(-\mathrm{SO}_3\mathrm{H}\), is another important acidic functional group. This group consists of a sulfur atom bonded to three oxygen atoms and has strong acidic properties, even more so than the carboxyl group.

• When a sulfonic group loses its hydrogen ion, it forms \(-\mathrm{SO}_3^-\).
• Sulfonic groups are commonly found in detergents and other similar substances due to their enhanced acidity and water solubility.

In the exercise, the sulfonic group's ability to lose a proton and form a negative charge complements the amino group's positive charge upon proton acceptance. This dual functionality makes such a pairing capable of forming a zwitterion. The robust acidic nature of the sulfonic group allows it to play a versatile role in numerous industrial and chemical processes.