Predict the organic products, in any order, when the alkene shown is subjected to ozonolysis with reductive work-up. Draw product 1. Draw product 2.
The Correct Answer and Explanation is:
The alkene shown in the image is 1-pentene, with the structure:
CH3-CH2-CH2-CH=CH2
When this alkene undergoes ozonolysis with reductive work-up (typically using reagents like O₃ followed by Zn/H₂O or dimethyl sulfide (DMS)), the double bond is cleaved and each carbon of the former double bond becomes the carbon of a carbonyl compound—specifically, an aldehyde if no further oxidation occurs.
Predicted Products:
The double bond in 1-pentene is between C-4 and C-5 in the chain. Breaking this double bond yields two fragments:
- Butanal (CH₃CH₂CH₂CHO)
- Formaldehyde (HCHO)
Structures:
Product 1: Butanal
A four-carbon aldehyde with the formula CH₃CH₂CH₂CHO
Product 2: Formaldehyde
A one-carbon aldehyde with the formula HCHO
Explanation
Ozonolysis is an oxidative cleavage reaction in which the carbon-carbon double bond of an alkene is broken and replaced with two carbonyl-containing fragments. In the presence of reductive work-up (such as zinc with water or dimethyl sulfide), the reaction yields aldehydes and/or ketones instead of carboxylic acids.
The compound shown is 1-pentene, an unbranched five-carbon alkene with a terminal double bond. Its structure is:
CH₃–CH₂–CH₂–CH=CH₂
During ozonolysis, ozone (O₃) adds to the double bond forming a molozonide intermediate, which rearranges to a more stable ozonide. The ozonide is then cleaved during the reductive work-up, resulting in two carbonyl products. Each carbon of the original double bond becomes the carbon of a carbonyl group.
For 1-pentene, the double bond lies between the fourth and fifth carbons. Cleavage of this double bond splits the molecule into:
- A four-carbon fragment (CH₃–CH₂–CH₂–) attached to the double-bonded carbon, which becomes butanal (CH₃CH₂CH₂CHO).
- A one-carbon fragment from the terminal carbon of the double bond, which becomes formaldehyde (HCHO).
These are the two organic products. Under oxidative work-up (e.g., H₂O₂), the aldehydes could further oxidize to carboxylic acids, but that is not the case here because the question specifies reductive work-up.
Thus, the final products are:
- Butanal
- Formaldehyde
These are the organic products formed from the ozonolysis of 1-pentene under reductive conditions.
