JEE Main 2021 · 20 July · evening · Single correct · +4 / −1
Which one of the following pairs of isomers is an example of metamerism?
- (a) CH₃CH₂CH₂CH₂CH₃ and CH₃; |; H₃C -, C, - CH₃; |; CH₃
- (b)
- (c)
- (d)
Answer and solution
Answer (d)
Solution
Chemistry ma’am · 3 steps
Metamerism needs the same polyvalent group, like C=O, with different alkyl groups on its two sides.
- What metamerism is. Metamers have the same molecular formula and the same functional group. That group sits between two alkyl groups, and the alkyl groups differ. It shows up in ethers, ketones, secondary amines and esters.
Option Pair What differs Type of isomerism (a) pentane and 2,2-dimethylpropane, both C₅H₁₂ the carbon skeleton chain (b) acetophenone and 3-phenylpropanal ketone versus aldehyde functional group (as drawn, the formulae C₈H₈O and C₉H₁₀O are not even the same) (c) 2-phenylethanol and 1-phenylethanol, both C₈H₁₀O position of the -OH on the side chain position (d) heptan-3-one and heptan-4-one, both C₇H₁₄O alkyl groups on the two sides of C=O metamerism - Check option (d). Heptan-3-one is CH₃CH₂-CO-CH₂CH₂CH₂CH₃: ethyl on one side, butyl on the other. Heptan-4-one is CH₃CH₂CH₂-CO-CH₂CH₂CH₃: propyl on both sides. The functional group is the same and only the alkyl groups around it are distributed differently.
- So. The ketone pair in (d), ethyl butyl ketone and dipropyl ketone, is the example of metamerism.
The idea to keep. For metamerism, look for a group joined to carbon on both sides (ether O, ketone C=O, NH, ester COO). Keep that group and the formula fixed, and change how the carbons are split between the two sides.
Answer from the NTA final answer key. Solution by PrepWiser.