Which is acidic in the given hydrocarbons ?

Options

A. `CH_3C-=CCH_3`
B. `CH_3CH_2CH_2CH_3`
C. `CH_3C-=CH`
D. `CH_2=CH-CH=CH_2`

Answer

To determine which hydrocarbon is the most acidic among the given options, we need to analyze the structure and hybridization of each compound. The acidity of hydrocarbons is influenced by the ability of the hydrogen atom to donate a proton (H⁺), which is affected by the electronegativity of the carbon atom to which the hydrogen is attached.

### Step-by-Step Solution:

1. **Identify the Hydrocarbons**:
- The hydrocarbons given are:
1. CH3C≡CCH3 (butyne)
2. CH3CH2CH2CH3 (butane)
3. CH3C≡CCH3 (butyne)
4. CH2=CH-CH2-CH3 (butene)

2. **Analyze Each Hydrocarbon**:
- **Option 1: CH3C≡CCH3 (butyne)**:
- This compound has a triple bond between carbon atoms. The hydrogen atoms attached to the sp hybridized carbon (the one involved in the triple bond) are more acidic due to the higher s-character (50%).

- **Option 2: CH3CH2CH2CH3 (butane)**:
- This compound is a straight-chain alkane with sp³ hybridized carbons. The hydrogen atoms here are less acidic because the s-character is only 25%, making the carbon less electronegative and thus less able to stabilize a positive charge.

- **Option 3: CH3C≡CCH3 (butyne)**:
- This is the same as option 1 and has the same reasoning. The hydrogen attached to the sp hybridized carbon is the most acidic due to its high s-character.

- **Option 4: CH2=CH-CH2-CH3 (butene)**:
- This compound has a double bond and is sp² hybridized. The hydrogen atoms here are less acidic than those in the sp hybridized carbon of butyne, as the s-character is 33.3%.

3. **Conclusion**:
- The most acidic hydrogen is found in the hydrocarbons with sp hybridized carbons, specifically in butyne (both instances). Therefore, the correct answer is **butyne (CH3C≡CCH3)**.

### Final Answer:
The most acidic hydrocarbon among the given options is **butyne (CH3C≡CCH3)**.