The ozonolysis of which one of the following alkenes yields a mixture

The ozonolysis of which one of the following alkenes yields a mixture of propan-2-one and formaldehyde?

Propene

Butene

2-Methylpropene

2-Methylbutene

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UPSC Geoscientist – 2023

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The correct answer is 2-Methylpropene.

Ozonolysis of an alkene involves the cleavage of the carbon-carbon double bond, yielding carbonyl compounds (aldehydes or ketones). The structure of the products dictates the structure of the original alkene. Propan-2-one has the structure (CH₃)₂C=O, and formaldehyde has the structure H₂C=O. For ozonolysis to yield these two products, the original alkene must have been (CH₃)₂C=CH₂.

(CH₃)₂C=CH₂ is 2-Methylpropene (also known as isobutylene). When the double bond is cleaved by ozonolysis, the carbon atom connected to two methyl groups forms a ketone (propan-2-one), and the CH₂ group forms an aldehyde (formaldehyde). Propene (CH₃CH=CH₂) yields acetaldehyde and formaldehyde. Butene can be but-1-ene (CH₃CH₂CH=CH₂, yields propanal and formaldehyde) or but-2-ene (CH₃CH=CHCH₃, yields acetaldehyde). 2-Methylbutene could be 2-methylbut-1-ene ((CH₃)₂C=CHCH₃, yields propan-2-one and acetaldehyde) or 2-methylbut-2-ene (CH₃C(CH₃)=CHCH₃, yields propan-2-one and acetaldehyde). Only 2-Methylpropene yields propan-2-one and formaldehyde.

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