Which cycloalkane has the highest boiling point? cyclopropane cyclobutane cyclopentane cyclohexane
The Correct Answer and Explanation is:1
Correct Answer: Cyclohexane
Explanation (Like in Textbooks):
The boiling points of cycloalkanes generally increase with an increase in the number of carbon atoms, due to greater molecular weight and surface area, which leads to stronger intermolecular forces—specifically, London dispersion forces (a type of van der Waals force). Let’s analyze the four cycloalkanes in question:
- Cyclopropane (C₃H₆)
- Molecular weight: 42.08 g/mol
- Boiling point: ~ -33°C
- Smallest ring; high ring strain due to 60° bond angles; lowest boiling point among the four.
- Cyclobutane (C₄H₈)
- Molecular weight: 56.11 g/mol
- Boiling point: ~ 12.5°C
- Slightly less ring strain than cyclopropane but still quite strained; slightly higher boiling point.
- Cyclopentane (C₅H₁₀)
- Molecular weight: 70.13 g/mol
- Boiling point: ~ 49.2°C
- Reduced ring strain and greater molecular weight; significantly higher boiling point than the previous two.
- Cyclohexane (C₆H₁₂)
- Molecular weight: 84.16 g/mol
- Boiling point: ~ 80.7°C
- Almost no ring strain due to its stable chair conformation; largest molecular surface area and strongest London dispersion forces; highest boiling point among the given options.
Boiling point is largely influenced by:
- Molecular weight – Heavier molecules have higher boiling points.
- Surface area – Larger surface area increases van der Waals attractions.
- Molecular structure – Molecules with more stable conformations and less strain allow tighter packing and stronger intermolecular forces.
Conclusion:
Among cyclopropane, cyclobutane, cyclopentane, and cyclohexane, cyclohexane has the highest boiling point due to its higher molecular mass, low ring strain, and greater van der Waals interactions. This trend aligns with general observations in homologous series of non-polar molecules.
