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Carbon tetravalency, shapes, hybridization and functional-group classification: NEET MCQs with answers

75 questions on this topic of Some Basic Principles of Organic Chemistry (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. In the molecule acetonitrile (CH₃-C≡N), what is the total number of σ (sigma) bonds and π (pi) bonds?

  1. 5 σ and 1 π
  2. 4 σ and 2 π
  3. 5 σ and 2 π
  4. 6 σ and 1 π
Show answer and explanation

Answer: (C) 5 σ and 2 π

The structural formula of acetonitrile is H₃C-C≡N. There are three C-H single bonds (3 σ), one C-C single bond (1 σ), and one C≡N triple bond (1 σ and 2 π). Thus, the total count is 5 σ bonds and 2 π bonds.

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2. Consider the following statements: Statement I: The C-C bond length decreases with an increase in the s-character of the participating hybrid orbitals. Statement II: An sp hybridized carbon orbital has higher energy and forms a longer bond than an sp³ hybridized carbon orbital. Choose the correct option:

  1. Both Statement I and Statement II are correct.
  2. Statement I is correct but Statement II is incorrect.
  3. Statement I is incorrect but Statement II is correct.
  4. Both Statement I and Statement II are incorrect.
Show answer and explanation

Answer: (B) Statement I is correct but Statement II is incorrect.

Statement I is correct because orbitals with higher s-character hold electron density closer to the nucleus, leading to shorter and stronger bonds. Statement II is incorrect because an sp orbital has higher s-character and lower energy than an sp³ orbital, leading to a shorter (not longer) bond.

hard

3. A straight-chain hydrocarbon has the molecular formula C₆H₆. If it contains two triple bonds and one double bond, how many carbon atoms in this molecule are sp hybridized and sp² hybridized, respectively?

  1. 2 sp and 4 sp²
  2. 4 sp and 2 sp²
  3. 3 sp and 3 sp²
  4. 4 sp and 1 sp²
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Answer: (B) 4 sp and 2 sp²

For a straight chain of 6 carbons to have two triple bonds and one double bond (such as hexa-3-en-1,5-diyne, HC≡C-CH=CH-C≡CH), each of the two triple bonds consists of two sp hybridized carbons (total 4 sp carbons). The single double bond involves two sp² hybridized carbons (total 2 sp² carbons).

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4. The degree of unsaturation (double-bond equivalent) of a compound with molecular formula C₅H₉Cl is:

  1. 3
  2. 1
  3. 2
  4. 0
Show answer and explanation

Answer: (B) 1

DBE = C − (H + X)/2 + N/2 + 1 = 5 − (9 + 1)/2 + 0/2 + 1 = 1. Oxygen does not change the DBE.

easy

5. Consider the following statements regarding the shapes and hybridization of carbon compounds: Statement I: Carbon in its excited state can form four equivalent covalent bonds directed towards the corners of a regular tetrahedron. Statement II: The C-C-C bond angle in cyclopropane is distorted significantly from the normal tetrahedral angle of 109.5°. In the light of the above statements, choose the most appropriate answer:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (A) Both Statement I and Statement II are correct

In its tetravalent state, sp³ hybridized carbon forms four equivalent bonds pointing toward the vertices of a regular tetrahedron with 109.5° bond angles. In cyclopropane, the ring is an equilateral triangle with internal C-C-C angles of 60°, which represents severe angle strain due to distortion from 109.5°.

hard

6. Match the pairs of atoms involved in the indicated bond in Column I with the type of orbital overlap in Column II: Column I P. C₂-C₃ bond in but-1-en-3-yne (CH₂=CH-C≡CH) Q. C-H bond in ethyne (HC≡CH) R. C₂-C₃ bond in propene (CH₃-CH=CH₂) S. C₁-C₂ bond in ethane (CH₃-CH₃) Column II 1. sp³-s 2. sp³-sp³ 3. sp²-sp 4. sp-s 5. sp³-sp² Choose the correct option:

  1. P-3, Q-4, R-5, S-2
  2. P-3, Q-1, R-5, S-2
  3. P-5, Q-4, R-3, S-2
  4. P-3, Q-4, R-2, S-5
Show answer and explanation

Answer: (A) P-3, Q-4, R-5, S-2

In but-1-en-3-yne (CH₂=CH-C≡CH), C2 is sp² and C3 is sp, so the C2-C3 bond is sp²-sp (P-3). In ethyne, the C-H bond involves an sp hybrid orbital of carbon and the 1s orbital of hydrogen, so sp-s (Q-4). In propene (CH₃-CH=CH₂), C2 is sp² and C3 is sp³, so the C2-C3 bond is sp³-sp² (R-5). In ethane (CH₃-CH₃), the C-C bond is sp³-sp³ (S-2).

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7. The degree of unsaturation (double-bond equivalent) of a compound with molecular formula C₄H₂NOCl is:

  1. 6
  2. 5
  3. 4
  4. 3
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Answer: (C) 4

DBE = C − (H + X)/2 + N/2 + 1 = 4 − (2 + 1)/2 + 1/2 + 1 = 4. Oxygen does not change the DBE.

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8. The degree of unsaturation (double-bond equivalent) of a compound with molecular formula C₁₀H₁₈O is:

  1. 1
  2. 3
  3. 2
  4. 4
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Answer: (C) 2

DBE = C − (H + X)/2 + N/2 + 1 = 10 − (18 + 0)/2 + 0/2 + 1 = 2. Oxygen does not change the DBE.

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9. The degree of unsaturation (double-bond equivalent) of a compound with molecular formula C₆H₇NOCl₂ is:

  1. 4
  2. 5
  3. 3
  4. 2
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Answer: (C) 3

DBE = C − (H + X)/2 + N/2 + 1 = 6 − (7 + 2)/2 + 1/2 + 1 = 3. Oxygen does not change the DBE.

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10. The degree of unsaturation (double-bond equivalent) of a compound with molecular formula C₁₀H₁₉N is:

  1. 4
  2. 2
  3. 1
  4. 3
Show answer and explanation

Answer: (B) 2

DBE = C − (H + X)/2 + N/2 + 1 = 10 − (19 + 0)/2 + 1/2 + 1 = 2. Oxygen does not change the DBE.

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11. Identify the compound that contains exactly two tertiary (3°) carbon atoms and no secondary (2°) carbon atoms.

  1. 2,3-Dimethylpentane
  2. 2,2-Dimethylbutane
  3. 2,3-Dimethylbutane
  4. 2-Methylbutane
Show answer and explanation

Answer: (C) 2,3-Dimethylbutane

2,3-Dimethylbutane has the formula (CH₃)₂CH-CH(CH₃)₂. The two central carbons (C2 and C3) are each bonded to three carbons, making them tertiary (3°). The remaining four carbons are methyl groups, which are primary (1°). It contains zero secondary (2°) carbons.

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12. The compound ethyl 2-cyanoacetate has the structure N≡C-CH₂-COOCH₂CH₃. Which of the following sets represents all the functional groups present in this molecule?

  1. Nitrile, ketone, and ether
  2. Nitrile and ester
  3. Nitrile and carboxylic acid
  4. Amine and ester
Show answer and explanation

Answer: (B) Nitrile and ester

The structure contains a cyano group (-C≡N), which is a nitrile, and an ethoxycarbonyl group (-COOCH₂CH₃), which is an ester. There is no free ketone, ether, amine, or carboxylic acid group.

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