The least reactive alkene towards hydrogenation is

Options

A.
B.
C.
D.

Explanation

To determine the least reactive alkene towards hydrogenation, we need to analyze the stability of the alkenes based on their substitution. Here’s a step-by-step solution:

### Step 1: Understand Hydrogenation and Alkene Reactivity
Hydrogenation is the process of adding hydrogen (H₂) to an alkene, converting it into an alkane. The reactivity of alkenes towards hydrogenation is influenced by their stability; more stable alkenes are less reactive.

### Step 2: Identify Alkene Substitution
Alkenes can be classified based on the number of alkyl groups attached to the carbon atoms of the double bond:
- Monosubstituted (1 alkyl group)
- Disubstituted (2 alkyl groups)
- Trisubstituted (3 alkyl groups)
- Tetrasubstituted (4 alkyl groups)

The more substituted the alkene, the more stable it is.

### Step 3: Count Alpha Hydrogens
Alpha hydrogens are the hydrogens attached to the carbon atoms adjacent to the double bond. The number of alpha hydrogens can give us an idea of the substitution level of the alkene.

1. **For the first alkene:**
- Double bond between two carbons, each with 3 hydrogens attached (CH₃-CH=).
- Total alpha hydrogens = 3 (from one carbon) + 3 (from the other carbon) = 6.

2. **For the second alkene:**
- Double bond between two carbons, each with 3 hydrogens attached (CH₃-CH=).
- Total alpha hydrogens = 3 + 3 = 6.

3. **For the third alkene:**
- Double bond between two carbons, with more complex substituents.
- Total alpha hydrogens = 3 (from one carbon) + 3 (from another) + 3 (from another) = 9.

### Step 4: Determine Stability and Reactivity
- The alkene with the highest number of alpha hydrogens is the most substituted and therefore the most stable.
- The most stable alkene will be the least reactive towards hydrogenation.

### Conclusion
Based on the analysis, the alkene with the most alpha hydrogens (and thus the most substitution) is the least reactive towards hydrogenation. Therefore, the answer is the alkene with the highest number of alpha hydrogens.

### Final Answer
The least reactive alkene towards hydrogenation is the one with the most substitution, which corresponds to option C.

---