Identify the alkyne in the following sequence of reactions:
Alkyne `overset(H_(2))underset("Lindlar's catalyst")to(A)overset("Ozonolysis")to(B)overset("Wacker")underset("Process")(larr) (H_(2)C)=CH_(2)`

Options

A. `H_(3)C-C-=C-CH_(3)`
B. `H_(3)C-CH_(2)-C-=CH`
C. `H_(2)C=CH-C-=CH`
D. `HC-=C-CH_(2)-C-=CH`

Answer

To identify the alkyne in the given sequence of reactions, we will follow the steps outlined in the video transcript and analyze the reactions systematically.

### Step-by-Step Solution:

1. **Understanding the Reaction Sequence**:
- We start with an alkyne, which undergoes hydrogenation in the presence of Lindlar's catalyst to form product A.
- Product A then undergoes ozonolysis to yield product B.
- Product B can be obtained through the Wacker process from ethylene (H₂C=CH₂).

2. **Identifying Product A**:
- The reaction of an alkyne with hydrogen in the presence of Lindlar's catalyst results in the formation of a cis-alkene.
- The general structure of an alkyne is R-C≡C-R. When hydrogen is added, it will convert the triple bond to a double bond, resulting in a cis configuration.
- Therefore, product A is a cis-alkene.

3. **Ozonolysis of Product A**:
- Ozonolysis involves the cleavage of the carbon-carbon double bond and the formation of carbonyl compounds (aldehydes or ketones).
- For a cis-alkene, ozonolysis will yield two carbonyl compounds. If we assume the alkene is symmetrical, we can denote it as R-C=C-R, which upon ozonolysis will yield R-C(=O)-H (aldehyde) on both sides.

4. **Identifying Product B**:
- The problem states that product B can be obtained through the Wacker process from ethylene (H₂C=CH₂).
- The Wacker process typically converts ethylene to acetaldehyde (CH₃CHO). This means that product B must be acetaldehyde.

5. **Determining the Original Alkyne**:
- Since product B is acetaldehyde and is derived from ozonolysis of product A, we need to find an alkyne that, when hydrogenated to a cis-alkene and then ozonolyzed, gives acetaldehyde.
- The alkyne that fits this description is 2-butyne (C₄H₆), which has the structure CH₃-C≡C-CH₃.
- Upon hydrogenation, it forms cis-2-butene (product A). Ozonolysis of cis-2-butene yields two molecules of acetaldehyde (product B).

6. **Final Conclusion**:
- The alkyne that fits all these criteria is 2-butyne (C₄H₆).

### Final Answer:
The alkyne in the sequence of reactions is **2-butyne**.