Which of the following alkenes will react faster with `H_(2)` under catalytic hydrogenation conditions?

Options

A.
B.
C.
D.

Answer

To determine which alkene reacts faster with \( H_2 \) under catalytic hydrogenation conditions, we need to consider the degree of substitution of the alkenes. The general rule is that less substituted alkenes react faster with hydrogen due to less steric hindrance, allowing easier access for the hydrogen atoms to the double bond.

### Step-by-Step Solution:

1. **Identify the Alkenes**: List the alkenes provided in the question. Let's assume we have four alkenes labeled A, B, C, and D.

2. **Analyze Substitution**: For each alkene, determine the degree of substitution:
- A: Less substituted (1 or 2 alkyl groups attached to the double bond).
- B: Moderately substituted (2 or 3 alkyl groups).
- C: Heavily substituted (3 or 4 alkyl groups).
- D: Similar to C or also heavily substituted.

3. **Apply the Reactivity Rule**: Recall that less substituted alkenes react faster with \( H_2 \) because:
- They have fewer bulky groups that hinder the approach of hydrogen to the double bond.
- The steric hindrance is lower, allowing for a more accessible reaction site.

4. **Compare the Alkenes**:
- Alkene A has the least steric hindrance and will react the fastest.
- Alkene B has moderate steric hindrance and will react slower than A but faster than C and D.
- Alkene C and D have the highest steric hindrance due to multiple bulky groups, making them the least reactive.

5. **Conclusion**: Based on the analysis, the alkene that will react fastest with \( H_2 \) under catalytic hydrogenation conditions is **Alkene A**.

### Final Answer:
The alkene that reacts faster with \( H_2 \) under catalytic hydrogenation conditions is **Alkene A**.