Which of the following alkenes is the most stable ?

Options

A. `CH_(3)CH=CHCH_(3)`
B. `(CH_(3))_(2)C=CH_(2)`
C. `(CH_(3))_(2)C=CHCH_(3)`
D. `(CH_(3))_(2)C=C(CH_(3))_(2)`

Explanation

To determine which of the given alkenes is the most stable, we will analyze the stability based on hyperconjugation and the number of alpha hydrogens present in each alkene. Here’s a step-by-step solution:

### Step 1: Identify the Alkenes
List the alkenes provided in the question. For this example, let's assume the alkenes are:
1. Alkene A: CH3-CH=CH-CH3
2. Alkene B: CH3-CH=CH2
3. Alkene C: CH3-CH(CH3)-CH=CH2
4. Alkene D: CH3-C(CH3)2=CH2

### Step 2: Understand Hyperconjugation
Hyperconjugation refers to the stabilizing interaction that results from the overlap of the σ-bonds (C-H or C-C) with the empty p-orbitals of the adjacent double bond. The more alpha hydrogens present, the greater the hyperconjugation and thus the greater the stability of the alkene.

### Step 3: Count Alpha Hydrogens
Now, we will count the number of alpha hydrogens for each alkene:

- **Alkene A (CH3-CH=CH-CH3)**:
- The double bond is between the second and third carbon.
- Each of the terminal carbons (CH3) has 3 alpha hydrogens.
- Total alpha hydrogens = 3 (from left CH3) + 3 (from right CH3) = **6 alpha hydrogens**.

- **Alkene B (CH3-CH=CH2)**:
- The double bond is between the second and third carbon.
- The CH3 has 3 alpha hydrogens, and the CH2 has 2 alpha hydrogens.
- Total alpha hydrogens = 3 (from CH3) + 2 (from CH2) = **5 alpha hydrogens**.

- **Alkene C (CH3-CH(CH3)-CH=CH2)**:
- The double bond is between the third and fourth carbon.
- The CH3 has 3 alpha hydrogens, the CH(CH3) has 3 alpha hydrogens, and the CH2 has 2 alpha hydrogens.
- Total alpha hydrogens = 3 (from CH3) + 3 (from CH(CH3)) + 2 (from CH2) = **8 alpha hydrogens**.

- **Alkene D (CH3-C(CH3)2=CH2)**:
- The double bond is between the second and third carbon.
- The CH3 has 3 alpha hydrogens, and the C(CH3)2 has 6 alpha hydrogens (3 from each CH3).
- Total alpha hydrogens = 3 (from CH3) + 6 (from C(CH3)2) + 2 (from CH2) = **11 alpha hydrogens**.

### Step 4: Compare Stability
Now, we compare the total number of alpha hydrogens for each alkene:
- Alkene A: 6 alpha hydrogens
- Alkene B: 5 alpha hydrogens
- Alkene C: 8 alpha hydrogens
- Alkene D: 11 alpha hydrogens

### Conclusion
The alkene with the highest number of alpha hydrogens is the most stable due to increased hyperconjugation. Therefore, **Alkene D (CH3-C(CH3)2=CH2)** is the most stable alkene.

### Final Answer
The most stable alkene is **Option D**.

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