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NEET CHEMISTRYHydrocarbonsEasy

Question

The linear molecule among the following is:

A

CH3−C≡C−CH3CH_3-C \equiv C-CH_3

B

CH2=CH−CH2−C≡CHCH_2=CH-CH_2-C \equiv CH

C

CH3−CH2−CH2−CH3CH_3-CH_2-CH_2-CH_3

D

CH3−CH=CH−CH3CH_3-CH=CH-CH_3

Step-by-Step Solution

  1. Hybridisation and Geometry: The shape of an organic molecule is determined by the hybridisation of its carbon atoms [NCERT 11th, Ch 12, Sec 12.3].
  • sp hybridisation: Bond angle = 180° (Linear).
  • sp² hybridisation: Bond angle = 120° (Trigonal Planar).
  • sp³ hybridisation: Bond angle = 109.5° (Tetrahedral).
  1. Analyze Option A (CH3−C≡C−CH3CH_3-C \equiv C-CH_3, 2-Butyne):
  • The central carbons (C2C_2 and C3C_3) are triply bonded. Triply bonded carbons are sp hybridised. This creates a linear arrangement of atoms along the C1−C2−C3−C4C_1-C_2-C_3-C_4 axis (180∘180^\circ bond angle).
  • While the methyl hydrogens are tetrahedral, the carbon skeleton itself is linear [NCERT 11th, Ch 13, Sec 13.4.2].
  1. Analyze Other Options:
  • Option B (CH2=CH−CH2−C≡CHCH_2=CH-CH_2-C \equiv CH): Contains sp2sp^2 (trigonal planar) and sp3sp^3 (tetrahedral) carbons, creating a bent/zigzag chain.
  • Option C (CH3−CH2−CH2−CH3CH_3-CH_2-CH_2-CH_3, n-Butane): All carbons are sp3sp^3 hybridised. The chain is zigzag (tetrahedral geometry at each carbon).
  • Option D (CH3−CH=CH−CH3CH_3-CH=CH-CH_3, 2-Butene): Contains sp2sp^2 carbons. The geometry around the double bond is trigonal planar, not linear.
  1. Conclusion: 2-Butyne is the linear molecule.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Hydrocarbons. 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.

CHEMISTRYHydrocarbonslinearmoleculefollowing

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