The most suitable reagent for the following conversion, is

Options

A. Zn/HCl
B. `Hg^(2+) // H^(+) , H_2O`
C. Na/liq. `NH_3`
D. `H_2`, Pd/C , quinoline

Answer

To determine the most suitable reagent for the conversion of an alkyne to a cis-alkene, we will analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Identify the Reaction**: We need to convert an alkyne into a cis-alkene. The specific type of alkene we want is a cis-alkene, which has the same groups on the same side of the double bond.

2. **Evaluate Option A (Zinc in HCl)**:
- Zinc in the presence of HCl produces hydrogen gas.
- This reaction typically leads to the reduction of the alkyne, converting it into an alkane (saturated compound).
- **Conclusion**: This reagent will not yield a cis-alkene; it will yield an alkane instead.

3. **Evaluate Option B (Mercuric Ion and Water)**:
- This reagent is used for hydration reactions, which add water across the triple bond of the alkyne.
- The product of this reaction would typically be a ketone or an alcohol, depending on the structure of the alkyne.
- **Conclusion**: This reagent does not produce a cis-alkene.

4. **Evaluate Option C (Sodium in Liquid Ammonia)**:
- Sodium in liquid ammonia is known to produce trans-alkenes from alkynes through a process called reduction.
- The product will be a trans-alkene, which is not what we are looking for.
- **Conclusion**: This reagent yields a trans-alkene, not a cis-alkene.

5. **Evaluate Option D (H2 in presence of Palladium, Quinoline)**:
- This reagent is known as the Lindlar catalyst.
- The Lindlar catalyst selectively hydrogenates alkynes to form cis-alkenes.
- The reaction proceeds without over-reduction to an alkane, yielding the desired cis-alkene.
- **Conclusion**: This is the correct reagent for converting an alkyne to a cis-alkene.

### Final Answer:
The most suitable reagent for the conversion of an alkyne to a cis-alkene is **H2 in the presence of Palladium, Quinoline (Lindlar Catalyst)**.

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