Isomerism

Isomerism MDCAT MCQs with answers

18 past paper MCQs on Isomerism, from the Fundamental Principles of Organic Chemistry unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.What are vinyl alcohol and acetaldehyde? (MDCAT 2023)

  1. position isomers
  2. chain isomers
  3. metamers
  4. tautomers
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Correct answer: (d) tautomers

They differ by the place of a hydrogen and a double bond and interconvert, which makes them tautomers.

2.1-Butene and 2-butene show which type of isomerism? (MDCAT 2024)

  1. functional group
  2. position
  3. metamerism
  4. chain
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Correct answer: (b) position

The chain and the functional group are the same in both; only the position of the double bond differs.

3.Which type of isomerism is displayed by compounds having the same structural formula but a different position of atoms on the two sides of a carbon-carbon double bond? (MDCAT 2024)

  1. chain
  2. metamerism
  3. geometric
  4. tautomerism
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Correct answer: (c) geometric

Restricted rotation about the double bond gives the cis and trans forms, which is geometric isomerism.

4.2-pentanone and 3-pentanone are examples of: (NUMS MDCAT 2025)

  1. Metamers
  2. Functional group isomers
  3. Tautomerism
  4. Position isomers
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Correct answer: (d) Position isomers

The two differ only in where the carbonyl group sits along the same chain.

5.Which compound will not show geometrical isomerism: (SIBA MDCAT 2025)

  1. But-2-ene
  2. 1,2-dimethylcyclopropane
  3. Pent-1-ene
  4. 1,3-dimethylcyclopentane
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Correct answer: (c) Pent-1-ene

Pent-1-ene has two hydrogens on its terminal carbon, so the two arrangements are the same.

6.Which one is not a type of stereoisomerism? (SIBA MDCAT 2025)

  1. Confirmational isomerism
  2. Optical isomerism
  3. Geometrical isomerism
  4. Metamerism
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Correct answer: (d) Metamerism

Metamerism is a kind of structural isomerism, not of stereoisomerism.

7.Which type of isomerism is displayed by compounds having same structural formula but different position of atoms on both sides of carbon bond? (UHS MDCAT 2024)

  1. Chain
  2. Metamerism
  3. Geometric
  4. Tautomerism
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Correct answer: (c) Geometric

Groups fixed on either side of a double bond give the cis and trans, or geometric, isomers.

8.Select the alkene showing geometrical isomerism: (NUMS MDCAT 2024)

  1. 3-methyl-1-butene
  2. Methyl cyclopentane
  3. 2,3-dimethyl-2-butene
  4. 3-methyl-2-pentene
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Correct answer: (d) 3-methyl-2-pentene

Each carbon of its double bond carries two different groups, which is what geometrical isomerism needs.

9.The type of isomerism arising due to shifting of proton fron one atom to another in the same molecule is: (SZABMU MDCAT 2023)

  1. Chain isomerism
  2. Metamerism
  3. Tautomerism
  4. Postion isomerism
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Correct answer: (c) Tautomerism

A proton shifting within the molecule between two forms in equilibrium is tautomerism.

10.The covalent compounds exhibit: (PMC MDCAT 2022)

  1. Fast reactions
  2. Non-directional nature
  3. Non-rigid structures
  4. lsomerism
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Correct answer: (d) lsomerism

A covalent bond points in a definite direction, so the same atoms can be arranged in more than one way.

11.Geometric isomerism is exhibited by: (NUMS MDCAT 2022)

  1. Alcohol
  2. Ethers
  3. Alkynes
  4. Alkenes
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Correct answer: (d) Alkenes

A double bond cannot rotate, so the groups on either side are fixed as cis or trans.

12.How many chain isomers of Pentane is possible? (PMC Practice 2021)

  1. Two
  2. Four
  3. Three
  4. Five
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Correct answer: (c) Three

Pentane, 2-methylbutane and 2,2-dimethylpropane are the three.

13.How many isomers of mono-substituted benzene are possible? (PMC Practice 2021)

  1. Two
  2. One
  3. Three
  4. None of these options is correct
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Correct answer: (b) One

All six positions of benzene are alike, so one substituent can be put in only one way.

14.The type of isomerism existing in a compound of molecular formula C2H6O is: (PMC MDCAT 2020)

  1. Functional group
  2. Position
  3. Chain
  4. Metamerism
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Correct answer: (a) Functional group

Ethanol and dimethyl ether share the formula but carry different functional groups.

15.Which of the following molecule shows cis- trans isomers? (UHS MDCAT 2019)

  1. C2H4
  2. C2H2Cl4
  3. C2H2Br2
  4. C2HCl3
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Correct answer: (c) C2H2Br2

1,2-dibromoethene has one substituent on each carbon of the double bond, so cis and trans differ.

16.Butane molecules can have a maximum number of isomers. (UHS MDCAT 2018)

  1. 5
  2. 3
  3. 4
  4. 2
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Correct answer: (d) 2

Butane and 2-methylpropane are the only two.

17.Name the compound, which shows geometric isomerism: (UHS MDCAT 2017)

  1. 1-bromo-2chloropropene
  2. 2-pentene
  3. 2,3-dimethyl propene
  4. Both “1-bromo-2 chloropropene” & “2-pentene”
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Correct answer: (d) Both “1-bromo-2 chloropropene” & “2-pentene”

Each carbon of the double bond in both carries two different groups.

18.Which one of the following pairs can be cis-trans isomer to each other? (UHS MDCAT 2016)

  1. CHCl=CCl2 and CH2=CH
  2. CHCl=CH2 and CH2=CHCl
  3. CH3CH=CHCH3 and H3CCH=CHCH3
  4. CH3CH3 and CH2=CH
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Correct answer: (c) CH3CH=CHCH3 and H3CCH=CHCH3

But-2-ene has a methyl and a hydrogen on each carbon of the double bond, so cis and trans differ.

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