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ChemistryIsomerismJEE · NEET
  1. 1. Isomer Basics
  2. 2. Functional
  3. 3. Metamerism
  4. 4. Keto-Enol
  5. 5. Other Tautomers
  6. 6. D.B.E. & Counting
  7. 7. Geometrical
  8. 8. Chirality
  9. 9. No Chiral Carbon
  10. 10. Counting Stereoisomers
  11. 11. Racemates & ee
  12. 12. Fischer & D/L
  13. 13. Alkane Conformations
  14. 14. Cyclohexane
Isomerism · Part 3 of 14

Metamerism

Metamers keep the same functional group but split their carbons differently on its two sides. Several pairs fit more than one label, so this part ends with the rules for choosing.

Builds on: Part 2 · Functional Isomerism.

Ethers

Same –O–, different sides

Diethyl ether (C₂ | O | C₂) and methyl propyl ether (C₃ | O | C₁) are both C₄H₁₀O ethers. The polyvalent group stays; the alkyl groups on its two sides change.

Two ether metamers.
The alkyl groups on each side are coloured.
Two ketone metamers.
Same C=O, different split.
Ketones

C₅H₁₀O

Diethyl ketone (pentan-3-one) and methyl propyl ketone (pentan-2-one). They are also position isomers: pick metamerism when it's offered.

Amines

Around –NH– and –N<

C₄H₁₁N: diethylamine / methyl propyl amine. C₅H₁₃N: dimethyl propyl amine / N-ethyl-N-methylethanamine.

Amine metamers.
Four amine metamers.
Three ester metamers.
Acyl side in blue, alkoxy side in orange.
Esters

Metamers of ethyl propionate

Ethyl propionate (C₂H₅COOC₂H₅) has the metamers propyl acetate (CH₃COOC₃H₇) and methyl butanoate (C₃H₇COOCH₃), all C₅H₁₀O₂ esters.

JEE-style question

Your turn

Metamers of ethyl propionate are:

(a)C₄H₉COOH and HCOOC₄H₉
(b)C₄H₉COOH and CH₃COOC₃H₇
(c)CH₃COOCH₃ and CH₃COOC₃H₇
(d)CH₃COOC₃H₇ and C₃H₇COOCH₃
Show the answer and the traps

Both must be esters of formula C₅H₁₀O₂: CH₃COOC₃H₇ and C₃H₇COOCH₃. Option (d).

(a) and (b) include an acid: a functional isomer, not a metamer. In (c), methyl acetate is C₃H₆O₂, a different formula.

Watch out

Common mistakes

Calling pentan-2-one and pentan-3-one only position isomers.They are metamers too; choose metamerism if it is offered.
Including an acid among metamers of an ester.An acid is a functional isomer; metamers keep the same functional group.
Practice

Try these

1. Which of the following are examples of metamerism? (a) Ethoxyethane and 1-methoxypropane (b) Pentan-2-one and pentan-3-one (c) N-Methylpropan-1-amine and N-ethylethanamine (d) All of the above

(d) All of the above (GRB Ch 4, Illustration Q3).

2. Write a metamer of diethylamine.

Methyl propyl amine (CH₃NHC₃H₇).

3. Are ethyl acetate and methyl propanoate metamers?

Yes: both C₄H₈O₂ esters with the carbons split differently around –COO–.

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