Which of the following has maximum extent of resonance?

Options

A. `R-overset(O)overset(||)(C)-Cl`
B. `R-overset(O)overset(||)(C)-O-overset(O)overset(||)(C)-R`
C. `R-overset(O)overset(||)(C)-OR`
D. `R-overset(O)overset(||)(C)-NH_(2)`

Answer

To determine which of the given compounds has the maximum extent of resonance, we will analyze the resonance structures of each compound based on the presence of lone pairs and the ability of atoms to donate electrons.

### Step-by-Step Solution:

1. **Understanding Resonance**:
- Resonance is a phenomenon where a molecule can be represented by two or more valid Lewis structures. These structures contribute to the overall stability of the molecule. The more resonance structures a molecule can have, the more stable it is.

2. **Identifying Compounds**:
- Let's denote the compounds as follows:
- Compound A: RCOCl (where R is an alkyl group)
- Compound B: RCOOH (carboxylic acid)
- Compound C: RCONH2 (amide)
- Compound D: RCOO- (carboxylate ion)

3. **Analyzing Each Compound**:
- **Compound A (RCOCl)**:
- Chlorine has a lone pair that can participate in resonance with the carbonyl group (C=O). However, chlorine is quite electronegative, which may limit its ability to donate electrons effectively.

- **Compound B (RCOOH)**:
- The carboxylic acid can show resonance between the carbonyl oxygen and the hydroxyl oxygen. However, the resonance is limited due to the presence of the acidic hydrogen, which does not participate in resonance.

- **Compound C (RCONH2)**:
- The amide can show resonance where the lone pair on nitrogen can delocalize into the carbonyl group. Nitrogen, being less electronegative than oxygen, can donate its lone pair effectively, allowing for some resonance.

- **Compound D (RCOO-)**:
- The carboxylate ion has two equivalent resonance structures where the negative charge can be delocalized between the two oxygen atoms. This delocalization significantly increases the resonance stabilization of the molecule.

4. **Comparing Resonance Extent**:
- Among the compounds analyzed:
- Compound A has limited resonance due to chlorine's electronegativity.
- Compound B has some resonance but is limited by the acidic hydrogen.
- Compound C has resonance due to nitrogen's lone pair but is less effective than the carboxylate.
- Compound D shows the maximum resonance due to the ability of the negative charge to be delocalized over two electronegative oxygen atoms.

5. **Conclusion**:
- Based on the analysis, **Compound D (RCOO-)** exhibits the maximum extent of resonance due to the effective delocalization of the negative charge over two oxygen atoms.

### Final Answer:
**The compound with the maximum extent of resonance is Compound D (RCOO-).**