Hyperconjugation is more pronounced in

Options

A. 2 - methylpropene
B. but -2-ene
C. 2,3 -dimethylbut - 2- ene
D. 2- methylbut -2-ene

Answer

To determine where hyperconjugation is more pronounced, we need to analyze the number of alpha-hydrogens in the given options. Hyperconjugation is a stabilizing interaction that results from the overlap of a σ-bond orbital with an adjacent empty or partially filled p-orbital or π-orbital. The more alpha-hydrogens present, the greater the hyperconjugation effect.

### Step-by-Step Solution:

1. **Understanding Hyperconjugation**:
- Hyperconjugation occurs when there are adjacent carbon atoms with hydrogen atoms (alpha-hydrogens) that can interact with a double bond or a positively charged carbon atom.
- The more alpha-hydrogens present, the stronger the hyperconjugation effect.

2. **Analyzing Each Option**:
- **Option A: 2-Methylpropene (C4H8)**:
- Structure: CH3-CH=C(CH3)-CH3
- Alpha-hydrogens:
- The double bond is between the second and third carbon.
- The first carbon has 3 alpha-hydrogens, the second carbon has 1, and the third carbon has 3.
- Total alpha-hydrogens = 3 + 1 + 3 = 7.

- **Option B: Butyrene (C4H8)**:
- Structure: CH3-CH=CH-CH3
- Alpha-hydrogens:
- The double bond is between the second and third carbon.
- The first carbon has 3 alpha-hydrogens, the second carbon has 1, the third carbon has 2, and the fourth carbon has 3.
- Total alpha-hydrogens = 3 + 1 + 2 + 3 = 9.

- **Option C: 2,3-Dimethylbutene (C6H12)**:
- Structure: CH3-CH=C(CH3)-C(CH3)-CH3
- Alpha-hydrogens:
- The double bond is between the second and third carbon.
- The second carbon has 1 alpha-hydrogen, the third carbon has 1 alpha-hydrogen, and each of the two methyl groups contributes 3 alpha-hydrogens.
- Total alpha-hydrogens = 1 + 1 + 3 + 3 + 3 = 11.

- **Option D: 2-Methyl-1-butene (C5H10)**:
- Structure: CH2=C(CH3)-CH2-CH3
- Alpha-hydrogens:
- The double bond is between the first and second carbon.
- The first carbon has 2 alpha-hydrogens, the second carbon has 3, and the third carbon has 2.
- Total alpha-hydrogens = 2 + 3 + 2 = 7.

3. **Comparison of Alpha-Hydrogens**:
- Option A: 7 alpha-hydrogens
- Option B: 9 alpha-hydrogens
- Option C: 11 alpha-hydrogens
- Option D: 7 alpha-hydrogens

4. **Conclusion**:
- The option with the maximum number of alpha-hydrogens is **Option C: 2,3-Dimethylbutene**, which has 11 alpha-hydrogens. Therefore, hyperconjugation is most pronounced in this compound.

### Final Answer:
**Option C: 2,3-Dimethylbutene** has the most pronounced hyperconjugation due to having the maximum number of alpha-hydrogens.