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 of each hydrocarbon and identify the acidic hydrogen atoms. Acidic hydrogens are typically those that can be easily removed as protons (H⁺), leading to the formation of stable anions. The stability of these anions is influenced by the hybridization of the carbon atom to which the hydrogen is attached.

### Step-by-Step Solution:

1. **Identify the Hydrocarbons**:
The hydrocarbons given are:
- Hydrocarbon 1: C≡C-H (alkyne)
- Hydrocarbon 2: CH3-CH2-CH2-CH3 (alkane)
- Hydrocarbon 3: CH3-C≡C-H (alkyne)
- Hydrocarbon 4: CH2=CH-CH2-CH3 (alkene)
- Hydrocarbon 5: CH=CH2 (alkene)

2. **Determine Hybridization**:
- For Hydrocarbon 1 (C≡C-H), the carbon is sp hybridized.
- For Hydrocarbon 2 (CH3-CH2-CH2-CH3), all carbons are sp³ hybridized.
- For Hydrocarbon 3 (CH3-C≡C-H), the terminal carbon is sp hybridized.
- For Hydrocarbon 4 (CH2=CH-CH2-CH3), the first two carbons are sp² hybridized and the last one is sp³.
- For Hydrocarbon 5 (CH=CH2), the first carbon is sp² hybridized and the second carbon is sp³.

3. **Identify Acidic Hydrogens**:
- Hydrocarbon 1 has one acidic hydrogen (H attached to sp carbon).
- Hydrocarbon 2 has no acidic hydrogen (all sp³).
- Hydrocarbon 3 has one acidic hydrogen (H attached to sp carbon).
- Hydrocarbon 4 has no acidic hydrogen (only sp² and sp³).
- Hydrocarbon 5 has one acidic hydrogen (H attached to sp² carbon).

4. **Analyze Stability of Anions**:
The stability of the anion formed after the removal of H⁺ is crucial:
- Anions formed from sp hybridized carbons (like in Hydrocarbons 1 and 3) are more stable due to higher s-character (50%).
- Anions formed from sp² hybridized carbons (like in Hydrocarbon 5) are less stable (33.3% s-character).
- Anions from sp³ hybridized carbons (like in Hydrocarbon 2) are the least stable (25% s-character).

5. **Conclusion**:
Hydrocarbons 1 and 3 have the most acidic hydrogens due to the sp hybridization. However, Hydrocarbon 3 (CH3-C≡C-H) is the most acidic because it has a terminal hydrogen attached to an sp carbon, making it more acidic than the other hydrocarbons.

### Final Answer:
The most acidic hydrocarbon is Hydrocarbon 3: CH3-C≡C-H.