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NEET CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques Medium

Question

Which of the following species contains an equal number of σ\sigma and π\pi bonds?

A

HCO3−HCO_3^-

B

XeO4XeO_4

C

(CN)2(CN)_2

D

CH2(CN)2CH_2(CN)_2

Step-by-Step Solution

  1. Analyze XeO4XeO_4: Xenon (Xe) has 8 valence electrons. It forms double bonds with four oxygen atoms to achieve a stable tetrahedral geometry. Each double bond consists of 1 σ\sigma bond and 1 π\pi bond.
  • Total σ\sigma bonds = 4
  • Total π\pi bonds = 4
  • Result: Equal number of σ\sigma and π\pi bonds .
  1. Analyze other options:
  • HCO3−HCO_3^- (Bicarbonate ion): The structure is HO−C(=O)−O−HO-C(=O)-O^-. It contains 4 σ\sigma bonds (C-O, C=O, C-O, O-H) and 1 π\pi bond (in C=O). (4σ,1π4\sigma, 1\pi)
  • (CN)2(CN)_2 (Cyanogen): The structure is N≡C−C≡NN \equiv C - C \equiv N. It contains 3 σ\sigma bonds (one C-C, two C-N) and 4 π\pi bonds (two in each C≡NC\equiv N triple bond). (3σ,4π3\sigma, 4\pi) .
  • CH2(CN)2CH_2(CN)_2 (Malononitrile): The structure is NC−CH2−CNNC-CH_2-CN. It contains 6 σ\sigma bonds (two C-H, two C-C, two C-N) and 4 π\pi bonds (two in each C≡NC\equiv N). (6σ,4π6\sigma, 4\pi)
  1. Conclusion: Only XeO4XeO_4 has an equal number of sigma and \pi bonds.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Organic Chemistry – Some Basic Principles and Techniques . Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

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