Question

A pair of compounds having the same boiling points are

• A. cis but-2-ene and trans but-2-ene
• B. n-hexane and neo-hexane
• C. Benzene and naphthalene
• D. (+) butan - 2 - ol and (-) butan - 2 - ol

Answer 1

The Correct Option is D

The boiling point of a compound is influenced by factors like molecular weight, intermolecular forces, and symmetry. Let's analyze the given options:

Option A: Benzene and Naphthalene 

This is incorrect. Benzene (C₆H₆) has a boiling point of 80.1°C, while naphthalene (C₁₀H₈) has a boiling point of 218°C. Hence, these two compounds do not have the same boiling points.

Option B: (+)-butan-2-ol and (-)-butan-2-ol

This is correct. Both (+)-butan-2-ol and (-)-butan-2-ol are enantiomers, which are non-superimposable mirror images. These compounds have the same molecular formula and identical intermolecular forces, which results in the same boiling points despite their optical isomerism.

Option C: cis-but-2-ene and trans-but-2-ene

This is incorrect. cis-but-2-ene and trans-but-2-eneare geometric isomers with different physical properties, including different boiling points. cis-but-2-ene has stronger intermolecular forces due to its molecular shape, leading to a higher boiling point than trans-but-2-ene.

Option D: n-hexane and neo-hexane

This is incorrect. n-hexane and neo-hexane are structural isomers, and while their molecular weight is similar, neo-hexane has a more compact structure, resulting in weaker intermolecular forces and a lower boiling point than n-hexane.

Conclusion:

The correct answer is: Option B: (+)-butan-2-ol and (-)-butan-2-ol, as they are enantiomers with the same boiling point.