In which of the following compounds is hydroxylic proton the most acidic ?

Options

A.
B.
C.
D.

Answer

To determine which compound has the most acidic hydroxylic proton, we need to analyze the stability of the resulting anion after the proton (H⁺) is removed. The more stable the anion, the more acidic the compound is.

Let's break down the steps:

### Step 1: Identify the Compounds
We have four compounds (A, B, C, D) with hydroxylic protons. We need to analyze each one to see how the structure affects the acidity.

### Step 2: Understand Acidity and Anion Stability
Acidity is related to the ability of a compound to donate a proton (H⁺). When a proton is lost, an anion is formed. The stability of this anion is crucial; a more stable anion corresponds to a more acidic compound.

### Step 3: Consider Inductive Effects
The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents in a molecule. Electron-withdrawing groups (EWGs) stabilize negative charges, while electron-donating groups (EDGs) destabilize them. We will focus on the -I (negative inductive) effect.

### Step 4: Apply the DNP Rule
The DNP rule (Distance, Number, Power) helps us prioritize the effects of substituents:
- **Distance**: Closer substituents have a stronger effect.
- **Number**: More substituents have a stronger effect.
- **Power**: More electronegative substituents have a stronger effect.

### Step 5: Analyze Each Compound
1. **Compound A**: Contains a fluorine substituent.
2. **Compound B**: Contains a fluorine substituent.
3. **Compound C**: Contains a fluorine substituent.
4. **Compound D**: Contains a fluorine substituent.

Since all compounds have fluorine, we need to assess the distance of the fluorine from the hydroxylic proton.

### Step 6: Determine the Most Acidic Compound
The compound with the fluorine closest to the hydroxylic proton will stabilize the negative charge best when the proton is lost. Therefore, we will find which compound has the fluorine closest to the hydroxyl group.

After analyzing the distances, it becomes clear that:
- **Compound D** has the fluorine closest to the hydroxylic proton, making it the most acidic due to the strong -I effect of fluorine stabilizing the resulting anion.

### Conclusion
The most acidic hydroxylic proton is found in **Compound D**.

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