Which one of the following orders of acidic strength is correct?

Options

A. `RCOOH gt HC -= CH gt HOH gt ROH`
B. `RCOOH gt ROH gt HOH gt HC -= CH`
C. `RCOOH gt HOH gt HC -= CH gt ROH`
D. `RCOOH gt HC -= CH gt HOH gt ROH`

Answer

To determine the correct order of acidic strength among the given compounds, we will analyze each compound's ability to donate a proton (H⁺) and the stability of the resulting anion after deprotonation.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Compound 1: R-C(=O)OH (Carboxylic acid)
- Compound 2: H-C≡C-H (Alkyne)
- Compound 3: H-O-H (Water)
- Compound 4: R-O-H (Alcohol)

2. **Analyze Compound 1 (Carboxylic Acid)**:
- When R-C(=O)OH donates H⁺, it forms R-C(=O)O⁻ (carboxylate ion).
- The negative charge on the carboxylate ion is stabilized by resonance, as it can be delocalized over the two oxygen atoms.
- **Conclusion**: This compound is highly acidic due to the resonance stabilization of the conjugate base.

3. **Analyze Compound 2 (Alkyne)**:
- When H-C≡C-H donates H⁺, it forms HC≡C⁻.
- The negative charge on the carbon in the alkyne is unstable due to high electron density and lack of resonance stabilization.
- **Conclusion**: This compound is less acidic because the resulting anion is unstable.

4. **Analyze Compound 3 (Water)**:
- When H-O-H donates H⁺, it forms OH⁻ (hydroxide ion).
- The hydroxide ion is relatively stable, but the electron-donating effect of the oxygen does not significantly stabilize it further.
- **Conclusion**: Water is moderately acidic.

5. **Analyze Compound 4 (Alcohol)**:
- When R-O-H donates H⁺, it forms R-O⁻.
- The negative charge on the alkoxide ion (R-O⁻) is less stable than that on the hydroxide ion (OH⁻) because the R group exerts a +I effect, which destabilizes the negative charge.
- **Conclusion**: Alcohols are less acidic than water.

6. **Order of Acidity**:
- Based on the analysis:
- R-C(=O)OH (Carboxylic acid) > H-O-H (Water) > R-O-H (Alcohol) > H-C≡C-H (Alkyne)
- Thus, the correct order of acidic strength is:
- RCOOH > H2O > ROH > HC≡CH

### Final Answer:
The correct order of acidic strength is:
**RCOOH > H2O > ROH > HC≡CH**