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:
To answer this question, we need to:
- Identify the product that results from ozonolysis followed by reductive workup (with dimethyl sulfide (DMS)).
- Work backward to deduce the original alkene structure.
- Ensure the alkene contains eight carbon atoms and produces only one product upon ozonolysis, which means the alkene is symmetrical or the cleavage results in identical products.
Step 1: Understanding Ozonolysis
Ozonolysis is a reaction where alkenes are cleaved at the double bond, and each carbon of the double bond is converted into a carbonyl group (either an aldehyde or ketone). When followed by dimethyl sulfide (DMS), the reaction yields aldehydes or ketones, not carboxylic acids.
Step 2: Drawing the Product
Let’s say the ozonolysis yields two molecules of butanal (CH₃CH₂CH₂CHO).
That would mean the double bond was between two butyl groups (CH₃CH₂CH₂–CH=CH–CH₂CH₂CH₃).
Step 3: Reconstructing the Alkene
Since ozonolysis cleaves the double bond and replaces each double-bonded carbon with a carbonyl oxygen, we reverse the process to find the original alkene.
Two molecules of butanal (CH₃CH₂CH₂CHO) would result from the cleavage of oct-4-ene, with the structure:
CH₃CH₂CH₂–CH=CH–CH₂CH₂CH₃
This is an eight-carbon (C₈) alkene. The double bond is between carbon 4 and 5, which is centrally located, and symmetrical, so ozonolysis yields only one product: butanal.
✅ Final Answer:
The correct structure is oct-4-ene:
CH₃–CH₂–CH₂–CH=CH–CH₂–CH₂–CH₃
Summary Explanation (300 words):
When an alkene undergoes ozonolysis followed by treatment with dimethyl sulfide (DMS), the double bond is cleaved, and each of the carbon atoms formerly involved in the double bond is converted into a carbonyl group. DMS is a reducing agent, so the carbonyl groups will be aldehydes or ketones, not carboxylic acids (which would form under oxidative conditions). The goal in this problem is to find an eight-carbon alkene that yields only one product after ozonolysis and reduction. This condition suggests that the molecule must be symmetrical, so the cleavage at the double bond produces identical fragments.
If the ozonolysis product is butanal (a four-carbon aldehyde), then two identical butanal molecules would combine to form the alkene. Reversing the ozonolysis process, we determine the original alkene was formed by joining the aldehyde groups via a double bond. Thus, the original compound must have had the structure CH₃CH₂CH₂–CH=CH–CH₂CH₂CH₃, which is oct-4-ene. It has a total of 8 carbon atoms and a double bond at the central position (between C-4 and C-5). When cleaved by ozone, it splits into two molecules of butanal. Because of its symmetry, no other products form, satisfying the condition in the problem. Hence, oct-4-ene is the only eight-carbon alkene that will yield a single ozonolysis product under these conditions.
Let me know if you’d like to see a diagram of the molecule.