Which of the following is weakest acid?

Options

A.
B.
C.
D.

Answer

To determine which of the given options is the weakest acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds**:
- We start by identifying the compounds provided in the options. They are likely derivatives of oic acids and benzoic acids with varying substituents.

2. **Understand the Role of Substituents**:
- The presence of substituents, especially electron-donating groups (EDGs) like -OH (hydroxyl group), affects the acidic strength of the compounds. EDGs decrease the acidity because they donate electrons to the aromatic ring, making it less likely to donate a proton (H⁺).

3. **Analyze the Hydroxyl Group**:
- The -OH group is a strong activating group due to its +R (resonance) and +I (inductive) effects. This means it can stabilize the negative charge that forms when the acid donates a proton, thus affecting the acidity.

4. **Evaluate the Position of the Hydroxyl Group**:
- The position of the -OH group is crucial:
- **Ortho Position**: Strong +R and +I effects, leading to significant electron donation, thus reducing acidity.
- **Para Position**: Also strong +R and +I effects, but more effective than ortho due to less steric hindrance.
- **Meta Position**: Only +I effect is present, which is less effective in stabilizing the negative charge compared to +R effects.

5. **Determine the Weakest Acid**:
- Since the compound with the -OH group at the para position will have the strongest electron-donating effect, it will be the weakest acid. The meta position will have a higher acidity than the para position since it does not have the resonance effect.

6. **Conclusion**:
- The compound with the -OH group at the para position is the weakest acid among the options provided.

### Final Answer:
The weakest acid is the one with the -OH group at the para position.

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