Ozonolysis of an unknown alkene gives one mole of $\text{HCHO}$ and one mole of ${\text{CH}}_3{\text{COCH}}_3$. What is the structure of the alkene?

Solution

1. Ozonolysis cleaves the $\text{C=C}$ bond to form carbonyl compounds.
2. The products are $\text{HCHO}$ (${\text{CH}}_2\text{=O}$) and ${\text{CH}}_3{\text{COCH}}_3$ (${\text{(CH}}_3{)}_2\text{C=O}$).
3. Reversing the process, we join the ${\text{CH}}_2$ group and the ${\text{(CH}}_3{)}_2\text{C}$ group with a double bond.
4. The resulting structure is ${\text{(CH}}_3{)}_2{\text{C=CH}}_2$, which is 2-methylpropene or isobutylene.
5. Hence the answer is (C).