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 determine the correct structure of an eight-carbon alkene that produces a single product after ozonolysis followed by dimethyl sulfide (DMS), we must understand the ozonolysis mechanism.
✅ Correct Answer:
The correct alkene is:
4-octene (CH₃CH₂CH=CHCH₂CH₂CH₃)
🧪 Product Formed After Ozonolysis with DMS:
Ozonolysis cleaves the C=C double bond, converting each carbon of the double bond into a carbonyl group (C=O). When using dimethyl sulfide (DMS) as the reducing agent, the ozonide intermediate is reduced to aldehydes or ketones, depending on substitution.
Let’s analyze 4-octene:
CH₃CH₂CH=CHCH₂CH₂CH₃
Carbon numbering:
1–CH₃
2–CH₂
3–CH=
4–CH
5–CH₂
6–CH₂
7–CH₃
The double bond is between carbon 4 and carbon 5.
🔬 Ozonolysis Reaction:
Ozonolysis cleaves the double bond and oxidizes both carbons into aldehydes or ketones:
From 4-octene:
CH₃CH₂CH₂–CHO (butanal)
and
CH₃CH₂CH₂–CHO (butanal)
✅ Both products are butanal, so only one compound is formed, making this the correct answer.
📘 Detailed Explanation (300+ Words):
Ozonolysis is a reaction where alkenes are cleaved by ozone (O₃), breaking the carbon–carbon double bond and forming carbonyl-containing compounds (aldehydes or ketones). The actual outcome depends on the substituents attached to the double bond and the work-up conditions. When using a reducing agent like dimethyl sulfide (DMS) in the second step, ozonolysis results in aldehydes or ketones, not carboxylic acids.
The problem specifies an eight-carbon alkene that yields only one product after ozonolysis with DMS. This implies the double bond must be symmetrically placed so that both halves of the molecule are identical after cleavage. If the alkene were asymmetrical, ozonolysis would produce two different products, violating the question’s constraint.
Among eight-carbon alkenes, 4-octene is symmetrically substituted. It has the structure CH₃CH₂CH=CHCH₂CH₂CH₃, with the double bond between carbon 4 and carbon 5. Upon ozonolysis, the double bond breaks, and each carbon forms a C=O group. In this case, both fragments are butanal (CH₃CH₂CH₂CHO), resulting in just one unique product.
Other alkenes like 1-octene or 2-octene would yield two different products (like formaldehyde and heptanal or propanal and pentanal) and thus do not meet the requirement.
Therefore, 4-octene is the only eight-carbon alkene that gives one ozonolysis product — butanal — when treated with ozone and dimethyl sulfide.