Question: 81: Compound X on reaction with \mathrm{O}_{3} followed by \mathrm{Zn}/\mathrm{H}_{2}\mathrm{O} gives formaldehyde and 2-methyl propanal as products. The compound X is
(1) 2-Methylbut-2-ene
(2) Pent-2-ene
(3) 3-Methylbut-1-ene
(4) 2-Methylbut-1-ene
Answer: Option (3)
Explanation:
Ozonolysis followed by reductive workup with \mathrm{Zn}/\mathrm{H}_{2}\mathrm{O} cleaves the carbon–carbon double bond to give carbonyl compounds.
Formation of formaldehyde indicates that one end of the double bond was a terminal
\mathrm{CH}_{2} group.
The other product is 2-methyl propanal, which has the structure
(\mathrm{CH}_{3})_{2}\mathrm{CHCHO}.
This implies that the other carbon of the double bond was attached to an isopropyl group.
Combining these two fragments, the original alkene must be
\mathrm{CH}_{2}=\mathrm{CHCH}(\mathrm{CH}_{3})\mathrm{CH}_{3},
which corresponds to 3-methylbut-1-ene.
Hence, the correct compound X is 3-methylbut-1-ene,
and the correct option is (3).