Chemistry · Isomerism
JEE Main 2026 — 24 January, Evening Shift — Question 66
Given below are two statements : one is labelled as Statement I and the other is labelled as Statement II :
Statement I : There are several conformers for n- butane. Out of those conformers, is (X) the least stable and most stable conformer is
Statement II : As the dihedral angle increases, torsional strain decreases from (X) to (Y).
In the light of the above statements, choose the correct answer from the options given below :
- Option A:
Both Statement I and Statement II are false
- Option B:
Statement I is false but Statement II is true
- Option C:
Statement I is true but Statement II is false
- Option D:Correct
Both Statement I and Statement II are true
Answer: D
Step-by-step solution
For n-butane, the conformers include eclipsed, gauche, and anti conformations. The least stable conformer is the fully eclipsed conformation (dihedral angle 0°) due to maximum torsional strain. The most stable conformer is the anti conformation (dihedral angle 180°) due to minimum torsional strain. Thus, Statement I is correct. Torsional strain arises from electron cloud repulsion between adjacent C-H bonds. As dihedral angle increases from 0° to 180°, the eclipsed bonds become staggered, reducing repulsion. Hence, torsional strain decreases from eclipsed (X) to anti (Y) conformation. Thus, Statement II is also correct. Therefore, both statements are true.
Answer key and solution verified before publishing.
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- Exam
- JEE Main 2026
- Subject
- Chemistry
- Chapter
- Isomerism
- Topic
- Conformational Isomerism