Draw the structure of an eight-carbon alkene that would yield the following compound (and no others) after treatment with ozone followed by dimethyl sulfide.
The Correct Answer and Explanation is:
Correct Answer:
The compound formed after ozonolysis is two molecules of butanal (CH₃CH₂CH₂CHO). The only eight-carbon alkene that yields exclusively this product is 3-octene.
Structure of 3-octene:
CH₃–CH₂–CH=CH–CH₂–CH₂–CH₂–CH₃
↑ ↑
C3 C4
Explanation
Ozonolysis is a powerful oxidative cleavage reaction that breaks double bonds in alkenes and forms carbonyl-containing products—either aldehydes or ketones. The outcome depends on the substituents attached to the alkene carbons. When the reaction is followed by a reducing agent such as dimethyl sulfide (DMS, (CH₃)₂S), aldehydes and ketones are formed instead of carboxylic acids.
The problem states that ozonolysis of an eight-carbon alkene produces a single product, and that product is butanal. Butanal is a 4-carbon aldehyde: CH₃CH₂CH₂CHO. Since ozonolysis cleaves the carbon-carbon double bond and converts each alkene carbon into a carbonyl group, the presence of two identical aldehydes implies that the double bond was symmetrically located in the alkene.
Let’s analyze 3-octene:
- Molecular formula: C₈H₁₆
- Double bond is between C3 and C4: CH₃–CH₂–CH=CH–CH₂–CH₂–CH₂–CH₃
- Upon ozonolysis, this double bond is cleaved, and each carbon becomes the carbon of an aldehyde group.
- The cleavage occurs between C3 and C4, forming:
- From C1–C3: CH₃–CH₂–CH (→ CHO) → CH₃CH₂CH₂CHO (butanal)
- From C4–C8: CH (→ CHO)–CH₂–CH₂–CH₃ → CH₃CH₂CH₂CHO (butanal)
Since both halves are the same, the only product is butanal.
Any other isomeric alkene (e.g., 2-octene, 4-octene) would result in either mixed aldehydes or ketones, violating the “no other products” condition. Therefore, 3-octene is the only correct structure that yields only butanal upon ozonolysis with DMS.
