Which one of the following compounds possesses the most acidic hydrogen?

Options

A. `H_(3)C-C-=C-H`
B.
C.
D.

Explanation

To determine which compound possesses the most acidic hydrogen, we need to analyze the stability of the resulting anion after the hydrogen ion (H⁺) is removed from each compound. The more stable the anion, the more acidic the hydrogen will be.

Let's go through the options step-by-step:

### Step 1: Identify the Compounds
Assume the compounds are:
1. Compound A: RCH₃ (alkane)
2. Compound B: RCH₂OH (alcohol)
3. Compound C: RCH₂CN (nitrile)
4. Compound D: RCOOH (carboxylic acid)

### Step 2: Analyze the Acidity of Each Compound
- **Compound A (Alkane)**: The hydrogen in alkanes is not very acidic. When it loses H⁺, it forms a carbanion (RCH₂⁻), which is highly unstable due to the lack of electronegative atoms nearby to stabilize the negative charge.

- **Compound B (Alcohol)**: The hydrogen in alcohols is more acidic than in alkanes. When it loses H⁺, it forms an alkoxide ion (RCH₂O⁻), which is stabilized by the electronegative oxygen atom.

- **Compound C (Nitrile)**: The hydrogen in nitriles is also more acidic. When it loses H⁺, it forms a carbanion (RCH₂CN⁻). The negative charge on the carbon can be stabilized by the electronegative nitrogen atom in the nitrile group through resonance.

- **Compound D (Carboxylic Acid)**: The hydrogen in carboxylic acids is the most acidic among the given options. When it loses H⁺, it forms a carboxylate ion (RCOO⁻). This anion is highly stabilized by resonance, as the negative charge can be delocalized between the two oxygen atoms.

### Step 3: Compare the Stability of the Resulting Anions
- Alkane anion (RCH₂⁻) is unstable.
- Alkoxide ion (RCH₂O⁻) is more stable than the alkane anion.
- Nitrile anion (RCH₂CN⁻) is also stable due to the presence of the electronegative nitrogen.
- Carboxylate ion (RCOO⁻) is the most stable due to resonance stabilization.

### Conclusion
Based on the analysis, the compound that possesses the most acidic hydrogen is **Compound D (Carboxylic Acid)**, as its corresponding anion (carboxylate) is the most stable.