Chemistry Hydrocarbons ETEA 2019
PMDC Verified Question 32 of 65
An olefin “X” on ozonolysis gives \( \text{CH}_3\text{CH}_2\text{COCH}_3 \) and \( \text{CH}_3\text{COCH}_3 \). The IUPAC name of X is:
A
2-Butane
B
2-Pentene
C
2-3 Di methyl-2-pentene
D
1-Hexene
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 2-3 Di methyl-2-pentene
Concept:

Ozonolysis cleaves a \( \text{C}=\text{C} \) double bond and replaces it with two \( \text{C}=\text{O} \) double bonds. The original alkene can be determined by mentally erasing the oxygens and stitching the two carbonyl carbons back together via a double bond.

Solution:

  • Product 1 is 2-butanone: \( \text{CH}_3\text{CH}_2-\text{C}(=\text{O})-\text{CH}_3 \).


  • Product 2 is acetone: \( \text{CH}_3-\text{C}(=\text{O})-\text{CH}_3 \).


  • Align the carbonyl groups: \( \text{CH}_3\text{CH}_2-\text{C}(\text{CH}_3)=\text{O} \) and \( \text{O}=\text{C}(\text{CH}_3)_2 \).


  • Remove the oxygens and connect the carbons with a double bond: \( \text{CH}_3\text{CH}_2-\text{C}(\text{CH}_3)=\text{C}(\text{CH}_3)_2 \).


  • Numbering the longest chain (5 carbons) to give the double bond and substituents the lowest numbers: 2,3-dimethyl-2-pentene.


Why other options are incorrect:

  • 2-butene and 2-pentene are straight-chain alkenes that would yield aldehydes, not ketones.


  • 1-hexene is a terminal alkene that yields formaldehyde and pentanal.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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