Ozonolysis and Formation of Acetone

Ozonolysis is a reaction where an alkene is cleaved by ozone (O₃) to form carbonyl compounds (aldehydes or ketones). The type of carbonyl compound produced depends on the substituents attached to the carbon atoms of the double bond.

Acetone is a ketone with the structure: ${CH}_{3} - C (= O) - {CH}_{3}$ . For acetone to be a product of ozonolysis, one carbon of the original double bond must have two methyl groups ( ${CH}_{3} -$ ) attached to it. This is represented by the general structure: ${CH}_{3} C_{2} =$ .

Step-by-Step Analysis of the Options

We will analyze each structure to see if its ozonolysis yields acetone.

Step 1: Analyze Option 1

Structure: 2,3-Dimethylbut-2-ene

Structure: ${CH}_{3} - C ({CH}_{3}) = C ({CH}_{3}) - {CH}_{3}$

Ozonolysis cleaves the central double bond. Each carbon of the double bond is identical and has one methyl and one hydrogen substituent. The products will be two molecules of acetone ( ${CH}_{3} - C (= O) - {CH}_{3}$ ). Therefore, acetone is a product.

Step 2: Analyze Option 2

Structure: 2-Methylbut-2-ene

Structure: ${CH}_{3} - C ({CH}_{3}) = C H - {CH}_{3}$

Ozonolysis cleaves the double bond. The products are acetone ( ${CH}_{3} - C (= O) - {CH}_{3}$ ) from one side and acetaldehyde ( ${CH}_{3} - C (= O) - H$ ) from the other. Therefore, acetone is a product.

Step 3: Analyze Option 3

Structure: Cyclopentene

Structure: A five-membered ring with one double bond.

Ozonolysis cleaves the double bond. Because the molecule is cyclic and symmetric, the product is a single dicarbonyl compound, a dialdehyde: OHC-(CH₂)₃-CHO. This does not contain acetone. Therefore, acetone is not a product.

Step 4: Analyze Option 4

Structure: 2,3-Dimethylbut-1-ene

Structure: ${CH}_{3} - C ({CH}_{3}) = C H - H$ or (CH₃)₂C=CH₂

Ozonolysis cleaves the double bond. The terminal carbon (=CH₂) will form formaldehyde (HCHO). The other carbon ( (CH₃)₂C= ) will form acetone ( ${CH}_{3} - C (= O) - {CH}_{3}$ ). Therefore, acetone is a product.

Final Answer: Options 1, 2, and 4 will give acetone as one of the products upon ozonolysis. Option 3 (Cyclopentene) will not.

Related Topics & Formulae

1. Ozonolysis Mechanism: The reaction occurs in two main steps.
Step 1: Ozonide formation: Alkene + O₃ → Molozonide → Ozonide.
Step 2: Reductive workup (e.g., with Zn/AcOH or SMe₂): Ozonide → Carbonyl compounds.

2. Predicting Ozonolysis Products:
A simple way to predict the products is to break the double bond (C=C) and replace each carbon with a terminal oxygen (=O).
General Rule: $R_{1} R_{2} C = C R_{3} R_{4}$ will yield $R_{1} R_{2} C = O$ and $R_{3} R_{4} C = O$ .

3. Key Theory:
- If a carbon of the double bond has two hydrogen atoms (e.g., R-CH=), it produces an aldehyde (R-CHO).
- If a carbon of the double bond has one hydrogen and one alkyl group (e.g., R₁R₂C=), it produces a ketone (R₁(C=O)R₂).
- A terminal =CH₂ group always produces formaldehyde (HCHO).