Question

Which of the following alkene on reductive ozonolysis gives ketones only as the product

• A. 1,2-butadiene
• B. 1,4-cyclohexadiene
• C. But-2-ene
• D. 2,3-dimethylbut-2-ene

Hint:

In ozonolysis, a double-bonded carbon with hydrogen gives aldehyde, while a double-bonded carbon without hydrogen gives ketone.

Answer 1

The Correct Option is D

Step 1: Understand reductive ozonolysis.
Reductive ozonolysis cleaves the carbon-carbon double bond of an alkene and forms carbonyl compounds.
If the double-bonded carbon contains hydrogen, aldehyde is formed.
If the double-bonded carbon has no hydrogen and is attached only to carbon groups, ketone is formed.

Step 2: Analyze the required condition.
To give ketones only, both carbon atoms of the double bond must not have any hydrogen atom attached to them.

Step 3: Analyze option (D).
In \( 2,3\text{-dimethylbut-2-ene} \), the structure is:
\[ (CH_3)_2C=C(CH_3)_2 \]
Both double-bonded carbon atoms are attached to methyl groups only and have no hydrogen atom.
Therefore, reductive ozonolysis gives only ketone, i.e. acetone.
\[ (CH_3)_2C=C(CH_3)_2 \xrightarrow[Zn/H_2O]{O_3} 2CH_3COCH_3 \]

Step 4: Check other options.
1,2-butadiene contains terminal carbon and may give aldehydic or other carbonyl products.
1,4-cyclohexadiene gives products containing aldehyde groups after cleavage.
But-2-ene has hydrogen atoms on both double-bonded carbons, so it gives aldehydes, not ketones only.

Step 5: Conclusion.
Only \( 2,3\text{-dimethylbut-2-ene} \) gives ketones only on reductive ozonolysis.
Therefore:
\[ \boxed{2,3\text{-dimethylbut-2-ene}} \]