Natural rubber on complete ozonolysis ( O3/Zn-H2O) gives compound X as the major product. X gives positive iodoform and Tollen's tests. X on heating with aqueous NaOH gives Y as the major product. Y is
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Answer
(1) [figure]
Solution
Natural rubber is cis-1,4-polyisoprene; ozonolysis ( O3/Zn-H2O) cleaves every C=C of the chain, so each isoprene unit gives one molecule of X:
[-CH2-C(CH3)=CH-CH2-]n O3/Zn-H2O [figure] (X, 4-oxopentanal)
X has a CH3CO- group (iodoform test +) and a CHO group (Tollens' test +).
[figure] aq. NaOH [figure]
The enolate of the CH3 group attacks the CHO carbon of the same molecule (intramolecular aldol; a 5-membered ring forms): 3-hydroxycyclopentanone.
[figure] [-H2O] [figure] (Y)
On heating the β-hydroxy ketone loses water to give the conjugated enone, cyclopent-2-en-1-one.
Answer: (A)