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 provide the correct structure of the eight-carbon alkene that yields a specific compound after ozonolysis followed by dimethyl sulfide, we need to break down the steps of the reaction and understand the mechanism of ozonolysis.
Ozonolysis Reaction Mechanism:
Ozonolysis is a reaction in which an alkene undergoes cleavage under the influence of ozone (O₃), resulting in the formation of two carbonyl compounds. The reaction proceeds through the following steps:
- Initial Ozone Addition: The alkene reacts with ozone, which adds to the double bond to form an unstable ozonide intermediate.
- Cleavage of the Ozonide: The ozonide intermediate then undergoes cleavage, forming two carbonyl-containing fragments.
- Workup with Dimethyl Sulfide: The ozonide is reduced with dimethyl sulfide (DMS), breaking the bond and resulting in aldehydes or ketones depending on the structure of the original alkene.
Key Observations:
- Ozonolysis of an alkene results in the cleavage of the double bond, yielding two carbonyl groups (aldehydes or ketones).
- The two carbonyl compounds formed should have a structure that is consistent with the original alkene’s structure.
Step-by-Step Approach:
- Compound Identification: The structure produced after ozonolysis will likely be two aldehydes or ketones depending on where the cleavage occurred in the original alkene. If the compound shows two aldehyde groups, it suggests the alkene was symmetric and the cleavage occurred at the middle of the double bond.
- Alkene Structure: Since the final compound has 4 carbonyl groups, the original alkene should have 8 carbon atoms to provide the proper cleavage pattern. This leads us to consider an internal symmetric eight-carbon alkene. The simplest structure that fits this criterion is 2,4-octadiene, which undergoes ozonolysis to produce two molecules of pentanal (C₅H₁₀O).
The Correct Alkene Structure:
The eight-carbon alkene that fits the requirement is 2,4-octadiene. Its structure is:
CH₂=CH-CH₂-CH=CH-CH₂-CH₂-CH₃This molecule undergoes ozonolysis, resulting in two molecules of pentanal:
CH₃-CH₂-CH₂-CHO (pentanal)Conclusion:
Thus, the correct alkene is 2,4-octadiene, and after ozonolysis followed by workup with dimethyl sulfide, it yields pentanal as the only product. This is the exclusive product, as the ozonolysis of 2,4-octadiene will always result in two identical aldehyde molecules.