Which of the following compounds can form a zwitterion?

Options

A. Aniline
B. Glycine
C. Benzoic acid
D. Acetanilide

Answer

To determine which of the given compounds can form a zwitterion, we need to understand the definition and characteristics of a zwitterion. A zwitterion is a molecule that has both positive and negative charges, resulting in a net charge of zero. This typically occurs in compounds that contain both an acidic group (which can donate a proton) and a basic group (which can accept a proton).

### Step-by-Step Solution:

1. **Understand the Definition of Zwitterion**:
- A zwitterion is a dipolar ion that has both a positive and a negative charge. This means that for a compound to form a zwitterion, it must have both acidic and basic functional groups.

2. **Analyze Each Compound**:
- **Aniline**: Aniline is a basic compound (an aromatic amine) with a nitrogen atom that can accept a proton (H+). However, it does not have an acidic group that can donate a proton. Therefore, it cannot form a zwitterion.
- **Glycine**: Glycine is an amino acid that contains both a carboxyl group (–COOH, which is acidic) and an amino group (–NH2, which is basic). In solution, glycine can lose a proton from the carboxyl group and gain a proton on the amino group, forming a zwitterion (NH3+ and COO−). Thus, glycine can form a zwitterion.
- **Benzoic Acid**: Benzoic acid contains a carboxyl group, which is acidic, but it does not have a basic group that can accept a proton. Therefore, it cannot form a zwitterion.
- **Acetonitrile**: Acetonitrile has a nitrile group (–CN) and does not have an acidic group that can donate a proton. It can only form a cation by accepting a proton, but it does not have a corresponding negative charge. Thus, it cannot form a zwitterion.

3. **Conclusion**:
- The only compound among the options that can form a zwitterion is **glycine**.

### Final Answer:
**Glycine** is the compound that can form a zwitterion.

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