Which do you think has a higher boiling point, pentane or neopentane (2,2-dimethylpropane)? Why?

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All right. Hi everyone. So this question says true or false. Butane has a higher boiling point than iso butane otherwise known as two methyl propane. So first, I want to go ahead and draw the structure of both compacts recall that butane is a straight chain of four carbons, whereas two methyl propane is a chain of three carbons and one methyl substituent in the metal. What I saw beauty and its important to understand the structure of these compounds because of how they affect the boiling point of each substance. Recall that the boiling point of a given substance is entirely dependent on the strength of that substance. Intermolecular forces or IMF for short, because during the boiling process, right, a liquid is being converted into a gas. So during that process, the intermolecular forces between molecules must be broken so that those molecules can move freely as a gas. So it makes sense to say then that the stronger the intermolecular force happens to be the higher the boiling point or BP for short is going to be right? Because if the IMF is stronger, more energy is required to break it during the boiling process. Now recall that because both butane and iso butane are nonpolar molecules specifically hydrocarbons, right? Their primary intermolecular force is going to be the London dispersion force. So we're going to compare and contrast for both molecules to see which of them has a stronger London London dispersion force than the other. Now, both butane and iso butane have the same number of carbon and hydrogen atoms. But their structure is of course different, right? Butane is a straight chain, whereas iso butane has a more branched structure as evidenced by the methyl substituent there. Now the dispersion force is heavily dependent on the surface area available for interaction. And what I mean by this is that the larger the surface area of a molecule is the more contact can be made with neighboring molecules which therefore strengthens the London dispersion force. So because butane is a straight chain molecule where is iso butin is branched, right. Butane is going to have more surface area a visible for interactions with neighboring molecules. And because of this, the London dispersion force and therefore its IMF is going to be stronger than that of iso butane. And like we discussed in the beginning of this video, the stronger the IMF the higher the boiling point is going to be. So all this is to say that the structure proposed or the statement proposed at the beginning of this video is actually true, right. Butane does have a higher boiling point than iso butane because there is a greater surface area available for interaction, its IMF s are going to be stronger and therefore the boiling point is higher. So with that being said, thank you so very much for watching. And I hope you found this helpful.

Which do you think has a higher boiling point, pentane or neopentane (2,2-dimethylpropane)? Why?

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Key Concepts

Boiling Point

Intermolecular Forces

Molecular Structure