Problem: Octane, C8H18 (bp: 125°C), boils nearly 35° higher than cyclooctane, C8H16 (bP : 90 °C): What are the primary factors responsible for the higher boiling point of octane? 

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For this problem, we are being asked to determine what are the factors that affect the difference of boiling point of octane and cyclooctane

Recall that there are several types of intermolecular forces (IMF):

1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF

2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF

3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF

4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF


Compounds with strong intermolecular forces have high boiling points. This is because they require more energy to be able to break the bonds during the phase transition.

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Problem Details

Octane, C8H18 (bp: 125°C), boils nearly 35° higher than cyclooctane, C8H16 (bP : 90 °C): What are the primary factors responsible for the higher boiling point of octane?