Question

Identify the reactant (A) in the given reaction

• A. 1-Methylcyclopentene (with double bond at C1-C2, methyl at C1)
• B. 3-Methylcyclopentene
• C. 1-Methylcyclopentene (alternative orientation)
• D. 1-Methylcyclohexene

Hint:

Ozonolysis of cyclic alkenes does not change the total number of carbon atoms.
Counting the total carbons in the product (6 carbons) and knowing it closed to a 5-membered ring with a methyl branch immediately rules out 3-methylcyclopentene and 1-methylcyclohexene.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We are given the product of the reductive ozonolysis of an alkene A.
The product is a keto-aldehyde (5-oxohexanal). We need to determine the structure of the starting cyclic alkene A.

Step 2: Key Formula or Approach:
The reductive ozonolysis of a cyclic alkene cleaves the double bond and yields a single dicarbonyl compound.
To reconstruct the reactant, we join the carbonyl carbon of the aldehyde group and the carbonyl carbon of the ketone group with a carbon-carbon double bond (C=C), which closes the ring.

Step 3: Detailed Explanation:

• Let us write out the structure of the product shown in the reaction:
The product is:
\[ \text{CH}_3-\text{C}(=\text{O})-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}=\text{O} \] This is 5-oxohexanal, containing 6 carbon atoms.

• Let us number the carbons of the chain to close the ring:
$\text{C}_1$ is the carbonyl carbon of the aldehyde (-CHO).
$\text{C}_2, \text{C}_3, \text{C}_4$ are the three methylene ($-\text{CH}_2-$) carbons.
$\text{C}_5$ is the carbonyl carbon of the ketone (-CO-).
$\text{C}_6$ is the terminal methyl carbon ($\text{-CH}_3$) attached to the ketone.

• To form the cyclic reactant, we remove the two carbonyl oxygen atoms and form a double bond between $\text{C}_1$ and $\text{C}_5$:
This forms a 5-membered ring containing $\text{C}_1, \text{C}_2, \text{C}_3, \text{C}_4,$ and $\text{C}_5$.
The double bond is between $\text{C}_1$ and $\text{C}_5$.
$\text{C}_6$ (the methyl group) remains attached to $\text{C}_5$.
The resulting structure is 1-Methylcyclopentene.

• Looking at the options, Option C shows a 5-membered ring with a double bond and a methyl group on one of the double-bonded carbons, representing 1-Methylcyclopentene.


Step 4: Final Answer:
The reactant A is 1-methylcyclopentene.