Chemistry Fundamental Principles of Organic Chemistry ETEA 2019
PMDC Verified Question 63 of 83
The number of isomers of pentane is:
A
2
B
4
C
5
D
3
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 3
Concept:

Pentane (\( \text{C}_5\text{H}_{12} \)) only exhibits chain isomerism. We must draw all possible unique carbon skeletons.

Solution:

  • 1. Straight chain (5 carbons): n-pentane.


  • 2. Branched chain with 4 carbons and one methyl group: isopentane (2-methylbutane).


  • 3. Branched chain with 3 carbons and two methyl groups: neopentane (2,2-dimethylpropane).


  • There are exactly 3 structural isomers possible.


Why other options are incorrect:

Butane has 2. Hexane has 5. Pentane definitively only has 3.

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