Properties and Uses of Unsaturated Hydrocarbons Answers

1-pentyne has a lower boiling point than 1-octyne because it has a shorter carbon chain and weaker intermolecular forces. Similarly, 1-butene has a higher vapor pressure at lower temperatures than 1-heptene because smaller molecules evaporate more easily. These differences occur because larger molecules have stronger London dispersion forces, meaning more energy is required to overcome these attractions to move the molecules from the liquid phase into the vapor phase.