Which of the following compounds is most acidic ?

Options

A. `CH_(4)`
B. `C_(2)H_(6)`
C. `CH-=CH`
D. `C_(2)H_(5)OH`

Answer

To determine which of the given compounds is the most acidic, we can analyze the acidity of each compound based on their structures and hybridization. The compounds provided are:

1. CH₄ (Methane)
2. C₂H₆ (Ethane)
3. C₂H₂ (Acetylene)
4. CH₃CH₂OH (Ethanol)

### Step-by-Step Solution:

**Step 1: Identify the hybridization of each compound.**
- **CH₄ (Methane)**: The carbon is sp³ hybridized (four single bonds).
- **C₂H₆ (Ethane)**: Each carbon is also sp³ hybridized (four single bonds).
- **C₂H₂ (Acetylene)**: Each carbon is sp hybridized (one triple bond and one single bond).
- **CH₃CH₂OH (Ethanol)**: The carbon atoms are sp³ hybridized, and the oxygen is sp³ hybridized as well.

**Hint for Step 1:** Look at the bonding and count the number of sigma bonds to determine hybridization.

**Step 2: Analyze the S-character of each compound.**
- **CH₄ and C₂H₆**: Both have 25% s-character (sp³).
- **C₂H₂**: Has 50% s-character (sp).
- **CH₃CH₂OH**: The carbon atoms have 25% s-character, but the presence of the hydroxyl (-OH) group increases acidity.

**Hint for Step 2:** Remember that higher s-character means greater electronegativity, which can lead to increased acidity.

**Step 3: Compare the acidity of the compounds.**
- **Methane (CH₄)** and **Ethane (C₂H₆)**: Both are very weak acids due to their sp³ hybridization and low s-character.
- **Acetylene (C₂H₂)**: More acidic than methane and ethane due to its sp hybridization and higher s-character.
- **Ethanol (CH₃CH₂OH)**: The presence of the hydroxyl group (–OH) makes it more acidic than acetylene because the hydrogen is bonded to oxygen, which is more electronegative than carbon.

**Hint for Step 3:** Consider the presence of functional groups like -OH that can significantly enhance acidity.

**Step 4: Conclusion**
Comparing all the compounds, ethanol (CH₃CH₂OH) is the most acidic due to the presence of the hydroxyl group which allows for better stabilization of the conjugate base after deprotonation.

**Final Answer:** The most acidic compound is **CH₃CH₂OH (Ethanol)**.