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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 Epxlanation is:
To solve this question, we need to work backwards from the ozonolysis product to identify the original alkene. Ozonolysis followed by treatment with dimethyl sulfide (DMS) is a reductive ozonolysis, which cleaves carbon-carbon double bonds and converts each carbon of the double bond into a carbonyl group (either an aldehyde or a ketone).
Let’s assume the ozonolysis product (which you didn’t specify) is a combination of carbonyl compounds that can only come from one specific alkene with eight carbon atoms.
Let’s suppose the ozonolysis gives two molecules of butanal (CH₃CH₂CH₂CHO). Each butanal has 4 carbon atoms. Since the ozonolysis cleaves a double bond and gives two carbonyl compounds, this suggests that the original alkene must have 8 carbon atoms, and the double bond is positioned symmetrically in the middle.
Structure of Butanal:
CH₃–CH₂–CH₂–CHO
Thus, two molecules of butanal (4C each) would make 8 carbon atoms total.
To yield two molecules of butanal, the original alkene must have the structure:
CH₃CH₂CH=CHCH₂CH₂CH₃
This is 3-octene, with the double bond between carbon 3 and 4. Upon ozonolysis, the double bond between C3 and C4 is cleaved, producing:
- From C1–C3: CH₃–CH₂–CH₂– (→ forms butanal)
- From C4–C8: –CH₂–CH₂–CH₂–CH₃ (→ also forms butanal)
So, ozonolysis of 3-octene gives only butanal, and no other products.
Correct Answer:
3-octene
Structure:
CH₃–CH₂–CH=CH–CH₂–CH₂–CH₃
Explanation (300+ words):
Ozonolysis is a powerful reaction used in organic chemistry to cleave carbon-carbon double bonds. When an alkene undergoes ozonolysis followed by treatment with a reducing agent like dimethyl sulfide (DMS), each carbon of the original double bond becomes the carbon of a carbonyl compound. Specifically, if the carbon had two hydrogen atoms, it forms formaldehyde; with one hydrogen and one alkyl group, it becomes an aldehyde; with two alkyl groups, it becomes a ketone.
To identify the original alkene, we must determine which double bond location would result in the observed ozonolysis products — in this case, only butanal, a four-carbon aldehyde.
To obtain two molecules of butanal from a single eight-carbon alkene, the double bond must be located symmetrically in the center of the chain. This ensures that the molecule is split evenly during ozonolysis. The structure that fits this description is 3-octene. It has a double bond between carbon 3 and carbon 4:
CH₃–CH₂–CH=CH–CH₂–CH₂–CH₃
When subjected to ozonolysis with DMS, the double bond between C3 and C4 is cleaved, and each resulting fragment gains an oxygen to form an aldehyde. The left fragment (C1–C3) forms butanal, and the right fragment (C4–C8) also forms butanal. Since no other carbonyl compounds are produced, and both products are identical, this confirms that 3-octene is the only correct alkene.
This is a classic retrosynthesis approach in organic chemistry, working backwards from the products to deduce the structure of the original molecule.