Classification of Organic Compounds

Classification of Organic Compounds MDCAT MCQs with answers

16 past paper MCQs on Classification of Organic Compounds, 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 is the molecular formula of the pyridine molecule? (MDCAT 2023)

  1. $\mathrm{C_6H_5N}$
  2. $\mathrm{C_5H_5N}$
  3. $\mathrm{C_4H_4N}$
  4. $\mathrm{C_6H_6N}$
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Correct answer: (b) $\mathrm{C_5H_5N}$

Pyridine is benzene with one CH replaced by N, so it is $\mathrm{C_5H_5N}$.

2.Homocyclic organic compounds are subdivided into two types, namely: (MDCAT 2024)

  1. alicyclic and aromatic
  2. alkenes and alkynes
  3. aromatic and non-aromatic
  4. saturated and unsaturated
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Correct answer: (a) alicyclic and aromatic

Rings of carbon only are either alicyclic, like cyclohexane, or aromatic, like benzene.

3.Pyridine belongs to which class of organic compounds? (KMU MDCAT 2024)

  1. Alicyclic
  2. Heterocyclic
  3. Homocyclic
  4. Hydrocarbon
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Correct answer: (b) Heterocyclic

Pyridine has a nitrogen atom in its ring, so it is heterocyclic.

4.Which of the following elements cannot be detected directly in a given organic compound? (KMU MDCAT 2024)

  1. Chlorine
  2. Nitrogen
  3. Oxygen
  4. Phosphorous
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Correct answer: (c) Oxygen

Oxygen has no test of its own; its presence is worked out from the difference in the analysis.

5.Homo-cyclic organic compounds are sub divided into two groups namely: (SZABMU MDCAT 2023)

  1. Alicyclic and Aromatic
  2. Open chain and branched chain
  3. Aromatic and non-aromatic
  4. Anti-aromatic
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Correct answer: (a) Alicyclic and Aromatic

A homocyclic ring of carbon alone is either alicyclic or aromatic.

6.Generic formula of cycloalkane is: (NUMS MDCAT 2023)

  1. CnH2n+2
  2. CnH2n
  3. CnH2n−1
  4. CnCH2n−2
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Correct answer: (b) CnH2n

A ring costs two hydrogens, so a cycloalkane is $\mathrm{C_nH_{2n}}$.

7.What is the molecular formula of pyridine molecule? (UHS MDCAT 2023)

  1. C6H5N
  2. C5H5N
  3. C5H5NH
  4. C6H6N
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Correct answer: (b) C5H5N

Pyridine is benzene with one carbon replaced by nitrogen, so its formula is $\mathrm{C_5H_5N}$.

8.Which of the following is not an IUPAC name of the compound? (PMC MDCAT 2022)

  1. Methanoic acid
  2. Ethanoic acid
  3. Propanoic acid
  4. Propionic acid
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Correct answer: (d) Propionic acid

Propionic acid is the trivial name; the systematic one is propanoic acid.

9.Which one of the following is not a common name? (PMC MDCAT 2022)

  1. Butanoic acid
  2. Formic acid
  3. Propionic acid
  4. Acetic acid
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Correct answer: (a) Butanoic acid

Butanoic acid is the systematic name; the others are the older trivial names.

10.Organic compounds in which tetravalency of carbon atom is satisfied are called as ____ ? (PMC Practice 2021)

  1. Saturated
  2. Unsaturated
  3. Alkenes
  4. Alkynes
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Correct answer: (a) Saturated

A compound with only single bonds has every valency of carbon used on a different atom, so it is saturated.

11.Friedrich prepared UREA from: (PMC Practice 2021)

  1. Amino acids
  2. Ammonium carbonate
  3. Ammonium cyanate
  4. Xanthin
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Correct answer: (c) Ammonium cyanate

Wohler made urea by heating ammonium cyanate, the first organic compound made from an inorganic one.

12.Which of the following is not a derivative of benzene? (PMC Practice 2021)

  1. Pyrrole
  2. Furan
  3. Thiophene
  4. All
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Correct answer: (d) All

Pyrrole, furan and thiophene are five membered heterocycles, not derivatives of benzene at all.

13.When are the prefixes ortho, para, and para used? (PMC Practice 2021)

  1. In alkynes to identify the position of the triple bond
  2. In arenes to identify the position of the first substitution
  3. In arenes to identify the position of the second substitution
  4. In all hydrocarbons to identify the position of the functional group
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Correct answer: (c) In arenes to identify the position of the second substitution

Ortho, meta and para say where the second substituent stands relative to the first.

14.Select the organic compound which belongs to Arene family: (PMC MDCAT 2020)

  1. CH2 = CH2
  2. CH3 – O – CH3
  3. CH3 – NH2
  4. C6H6
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Correct answer: (d) C6H6

Benzene is the parent of the arenes.

15.IUPAC name of C6H5 – CH2 – CH2 – NH2 is: (PMC MDCAT 2020)

  1. 2-phenyl ethenamine
  2. 2-phenyl ethanamine
  3. 2-phenyl ethylamine
  4. 3-phenyl ethanamine
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Correct answer: (b) 2-phenyl ethanamine

The chain is ethane with an amino group on carbon 1 and a phenyl group on carbon 2.

16.Cyclobutane structure is categorized under: (UHS MDCAT 2017)

  1. Aromatic compounds
  2. Alicyclic compounds
  3. Aliphatic compounds
  4. Heterocyclic compounds
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Correct answer: (b) Alicyclic compounds

Cyclobutane is a saturated carbon ring with no aromatic character, so it is alicyclic.

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