Question

What are the final products obtained by ozonolysis of propene?

• A. 2 molecules of acetaldehyde
• B. acetone
• C. 2 molecules of formaldehyde
• D. formaldehyde and acetaldehyde

Hint:

To predict ozonolysis products instantly, conceptually clear out the double bond ($\mathrm{C=C}$) with an eraser, separate the fragments, and attach a double-bonded oxygen ($=\mathrm{O}$) to each exposed carbon tail. Propene gives a 2-carbon aldehyde (acetaldehyde) and a 1-carbon aldehyde (formaldehyde).

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The problem requires identifying the final carbonyl compounds generated upon the complete reductive ozonolysis of propene ($\mathrm{CH}_3\mathrm{CH=CH}_2$).

Step 2: Key Formula or Approach:
Ozonolysis involves the cleavage of an unsaturated carbon-carbon double bond ($\mathrm{C=C}$) using ozone ($\mathrm{O}_3$), followed by reductive workup (typically using $\mathrm{Zn/H}_2\mathrm{O}$). The overall process cleanly breaks the double bond and appends an oxygen atom to each of the two original olefinic carbons:
$$\mathrm{R_1CH=CHR_2} \xrightarrow{[1]\ \mathrm{O}_3,\ [2]\ \mathrm{Zn/H}_2\mathrm{O}} \mathrm{R_1CHO} + \mathrm{R_2CHO}$$

Step 3: Detailed Explanation:
Let's write down the structural formula of propene:
$$\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}_2$$ During the first step, ozone adds across the double bond to form an unstable cyclic ozonide intermediate.
In the subsequent reductive cleavage step with zinc dust and water, the ozonide ring is broken down right across the original double bond line:
1. The left-hand segment containing two carbons ($\mathrm{CH}_3-\mathrm{CH=}$) turns into acetaldehyde ($\mathrm{CH}_3\mathrm{CHO}$).
2. The right-hand segment containing a single carbon ($=\mathrm{CH}_2$) turns into formaldehyde ($\mathrm{HCHO}$).
The overall reaction can be summarized as:
$$\mathrm{CH}_3\mathrm{CH=CH}_2 + \mathrm{O}_3 \xrightarrow{\mathrm{Zn/H}_2\mathrm{O}} \mathrm{CH}_3\mathrm{CHO} + \mathrm{HCHO}$$

Step 4: Final Answer:
The final products are formaldehyde and acetaldehyde, matching option (D).