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JEE Advanced 2026Paper 2
Exam
JEE Advanced
Year
2026
Paper
Paper 2
Subject
Chemistry
Chapter
Hydrocarbons

JEE Advanced 2026 · Paper 2 · Chemistry · Hydrocarbons

Natural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives...

Natural rubber on complete ozonolysis (O3\text{O}_3/Zn-H2O\text{H}_2\text{O}) gives compound X\textbf{X} as the major product. X\textbf{X} gives positive iodoform and Tollen's tests. X\textbf{X} on heating with aqueous NaOH gives Y\textbf{Y} as the major product. Y\textbf{Y} isNatural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positiveNatural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positiveNatural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positiveNatural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positiveNatural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positive

Options

  1. AThe concentration of dissolved Oxygen in water for growth of fish should be more than X _ ¯ ppm and Biochemical Oxygen
  2. BThe concentration of dissolved Oxygen in water for growth of fish should be more than X _ ¯ ppm and Biochemical Oxygen
  3. CThe concentration of dissolved Oxygen in water for growth of fish should be more than X _ ¯ ppm and Biochemical Oxygen
  4. DThe concentration of dissolved Oxygen in water for growth of fish should be more than X _ ¯ ppm and Biochemical Oxygen

Correct answer

A. The concentration of dissolved Oxygen in water for growth of fish should be more than X _ ¯ ppm and Biochemical Oxygen

Step-by-step solution

Natural rubber is cis-1,4-polyisoprene, with the repeating unit [−CH2−C(CH3)=CH−CH2−]n[-\text{CH}_2-\text{C}(\text{CH}_3)=\text{CH}-\text{CH}_2-]_n.

Complete reductive ozonolysis (O3\text{O}_3/Zn-H2O\text{H}_2\text{O}) of natural rubber cleaves the double bonds to give 4-oxopentanal (levulinaldehyde) as compound X.

[−CH2−C(CH3)=CH−CH2−]n→O3/Zn-H2On CH3−C(=O)−CH2−CH2−CHO[-\text{CH}_2-\text{C}(\text{CH}_3)=\text{CH}-\text{CH}_2-]_n \xrightarrow{\text{O}_3/\text{Zn-H}_2\text{O}} n \text{ CH}_3-\text{C}(=\text{O})-\text{CH}_2-\text{CH}_2-\text{CHO}

Compound X (CH3−CO−CH2−CH2−CHO\text{CH}_3-\text{CO}-\text{CH}_2-\text{CH}_2-\text{CHO}) has a methyl ketone group, which gives a positive iodoform test, and an aldehyde group, which gives a positive Tollen's test.

When X is heated with aqueous NaOH, it undergoes an intramolecular aldol condensation. The base abstracts an α\alpha-proton from the terminal methyl group to form an enolate, which then attacks the aldehyde carbonyl carbon to form a stable five-membered ring.

The intermediate formed is 3-hydroxycyclopentanone, which upon heating undergoes dehydration to yield cyclopent-2-en-1-one as the major product Y.

Answer: Natural rubber on complete ozonolysis ( O_3 /Zn- H_2O ) gives compound X as the major product. X gives positive
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