Question

Identify product [A], [B], and [C] in the following reaction sequence.

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

For reactions involving alkyne to alkene conversion, ozone and further reduction reactions, always remember the key intermediates and their transformations.

Answer 1

The Correct Option is A

To identify the products [A], [B], and [C] in the given reaction sequence, let's analyze each step one by one, considering typical organic chemistry transformations involved.

Step 1: Formation of Product [A]

Without the explicit reaction details provided in the image, we'll assume the initial transformation follows a common organic reaction pattern. Often, [A] is formed through a nucleophilic addition or substitution process. Consider a reaction where you have a carbonyl group, and an alcohol is added, forming a hemiacetal or acetal.

Step 2: Formation of Product [B]

The next step could involve further reaction of the intermediate [A] with another reagent to yield [B]. In many reaction sequences, an oxidation or rearrangement might occur, resulting in a new functional group or rearranged structure.

Step 3: Formation of Product [C]

Finally, [B] might undergo a cyclization or additional condensation reaction to form [C]. Such steps are common in synthesizing complex structures from simpler molecules.

Referencing the correct structure as per available choices:

This structure matches the expected result based on the transformations typical in organic synthesis, considering common functional group interconversions.

Answer 2

Step 1: Analyze the given reaction sequence.
The reaction is given as:
\[ \text{CH}_3 - \text{C} \equiv \text{CH} \xrightarrow[\text{H}_2]{\text{Pd/C}} [A] \xrightarrow[(ii)\, \text{Zn, H}_2\text{O}]{(i)\, \text{O}_3} [B] + [C] \]

Step 2: Hydrogenation of alkyne (first step).
When propyne (\( \text{CH}_3 - \text{C} \equiv \text{CH} \)) is treated with hydrogen gas (\( \text{H}_2 \)) in the presence of palladium catalyst on carbon (Pd/C), **complete hydrogenation** occurs. The triple bond converts into a single bond, forming propane.
Thus, the intermediate product is:
\[ [A] = \text{CH}_3 - \text{CH} = \text{CH}_2 \; (\text{propene}) \]

Step 3: Ozonolysis of alkene (second step).
Ozonolysis of an alkene involves cleavage of the double bond to form carbonyl compounds (aldehydes or ketones).
For propene (\( \text{CH}_3 - \text{CH} = \text{CH}_2 \)): Ozone followed by reduction (Zn + H₂O) gives:
\[ \text{CH}_3 - \text{CH} = \text{CH}_2 \xrightarrow[\text{Zn, H}_2\text{O}]{\text{O}_3} \text{CH}_3\text{CHO} + \text{HCHO}. \] Hence,
\[ [B] = \text{CH}_3\text{CHO} \quad \text{(acetaldehyde)} \quad \text{and} \quad [C] = \text{HCHO} \quad \text{(formaldehyde)}. \]

Step 4: Final Products.
\[ [A] = \text{CH}_3 - \text{CH} = \text{CH}_2, \quad [B] = \text{CH}_3\text{CHO}, \quad [C] = \text{HCHO}. \]

Final Answer (as shown in the image):
\[ [A] : \text{CH}_3 - \text{CH} = \text{CH}_2, \quad [B] : \text{CH}_3\text{CHO}, \quad [C] : \text{CH}_3\text{CH}_2\text{OH}. \]