Which of the following reagent not gives syn addition when react with alkyne.

Options

A. `H_(2) + Pd` (`CaCO_(3) +` Quinoline)
B. P — 2 catalyst
C. Raney Nickel
D. Li/liq. `NH_(3)`

Answer

To determine which reagent does not give syn addition when reacting with an alkyne, we can analyze the behavior of different reagents with alkynes.

### Step-by-Step Solution:

1. **Understanding Syn Addition**:
- Syn addition refers to the addition of two substituents to the same side of a double bond or triple bond. In the case of alkynes, this means that when hydrogen is added across the triple bond, both hydrogen atoms will add to the same side of the resulting double bond.

2. **Analyzing Different Reagents**:
- **Palladium Catalyst (Pd)**: When an alkyne reacts with hydrogen in the presence of a palladium catalyst, syn addition occurs. The hydrogen atoms are added to the same side of the alkyne, resulting in a cis-alkene.

- **Nickel Catalyst (Ni)**: Similar to palladium, nickel also facilitates syn addition when reacting with alkynes. The addition of hydrogen occurs on the same side, leading to a cis-alkene.

- **Birch Reduction (Liquid Ammonia with Lithium)**: The Birch reduction involves the reaction of alkynes with lithium in liquid ammonia. This process leads to the formation of a trans-alkene rather than a cis-alkene. The mechanism involves the formation of a vinylic radical, which results in the trans addition of hydrogen atoms.

3. **Conclusion**:
- Among the reagents discussed, the Birch reduction does not result in syn addition. Instead, it yields a trans-alkene. Therefore, the reagent that does not give syn addition when reacting with an alkyne is the Birch reduction (option 4).

### Final Answer:
The reagent that does not give syn addition when reacting with an alkyne is **Birch reduction (Liquid Ammonia with Lithium)**.

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