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MCQEasyJEE 2026Isomerism (Structural, Stereoisomerism)

JEE Chemistry 2026 Question with Solution

Given below are two statements regarding conformations of n-butane. Choose the correct option.

Required conformation diagram for n-butane statements is missing from the source, so the two labeled statements are not visible.
  • A

    Both Statement I and Statement II are false

  • B

    Statement I is false but Statement II is true

  • C

    Statement I is true but Statement II is false

  • D

    Both Statement I and Statement II are true

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: Two statements regarding conformations of n-butane are to be checked.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

From the extracted solution:

  1. Stability of conformers: In n-butane, the eclipsed conformation is the least stable due to maximum torsional strain, while the anti-staggered conformation is the most stable.
  2. Effect of dihedral angle: As the dihedral angle increases from eclipsed to staggered, torsional strain decreases, so stability increases.
  3. Therefore, both statements are correct according to the solution.

The correct option is D.

Note: The actual two statements are not visible in the given question because the required image/content is missing, but the solution explicitly concludes that both statements are true.

Common mistakes

  • Assuming that every staggered conformation of n-butane has the same stability is incorrect. The anti-staggered form is more stable than the gauche form because steric repulsion is minimum in the anti arrangement.

  • Confusing torsional strain with general steric crowding can lead to wrong conclusions. For conformational comparison, first check whether the conformation is eclipsed or staggered, then compare relative repulsions.

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