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Which of the following compounds has the highest boiling point?

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Correct Answer: B. Octane.
The boiling point of hydrocarbons increases as the number of carbons increases. Therefore, Heptane has a higher boiling point than hexane, which has a higher boiling point than pentane. This is because the intermolecular forces between molecules keep the hydrocarbons in solution, requiring more heat to overcome these forces and become a gas. In the case of branched molecules, the hydrocarbons are not able to “stack” as easily as straight-chain hydrocarbons. This reduces intermolecular interactions and, subsequently, the boiling point. Even though octane, 2,2-dimethylhexane, and 2-methylheptane have eight carbons, octane has the highest boiling point.
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