Arrange the following compounds in order of increasing boiling point. Explain why you placed them in that order.
a.

Question

Arrange the following compounds in order of increasing boiling point. Explain why you placed them in that order.

a.

Accepted Answer

All right. Hi everyone. So this question says to consider the following molecules of which there are three list them in order of decreasing boiling point and justify your answer. Here we have four different answer choices. Each proposing a different order, a different arrangement of the three as well as different reasons for the trend. No. Based on the answer choices provided what I want to point out here is that all of them discuss the effect of intermolecular forces or IMF S on the boiling or melting point of a substance. Recall that IMF S are interactions between molecules that keep them in close proximity to each other. So during the boiling process, for example, when converting a substance from a liquid to a gas, then those IMF s have to be broken so that these molecules can move freely away from each other, right? So it makes sense to say that the stronger an intermolecular force is the higher the boiling point of that substance is going to be right? Because it would make sense that more energy is required to break a stronger interaction. Now, polar molecules are capable of stronger IMF s than nonpolar molecules but considering the structures of the three molecules provided two are a means and one is an alcohol. So because of this, all three are polar molecules, so we can consider the three main intermolecular forces experienced by polar compound. The strongest of which is the ion dipole interaction in which an ion interacts or interacts with a polar covalent bond. Now, the second strongest IMF is going to be hydrogen bonding and hydrogen bonding is experienced with molecules that contain hydrogen atoms bound to highly electron atoms like nitrogen, oxygen or fluorine. And then the third strongest IMF would be the dile dile interaction in which two polar covalent bonds interact with each other. So if we consider the structures of the three molecules provided, recall how previously I mentioned that in order for a substance to be capable of of hydrogen bonding, there has to be a hydrogen atom attached to electron atoms such as not nitrogen, oxygen and fluorine. And considering the structures of molecules one and three compound one has hydrogen attached to nitrogen, whereas compound three has hydrogen attached to oxygen. So both of these molecules are therefore capable of hydrogen bonding, whereas the second molecule is also an amine, but there's no hydrogen attached to nitrogen. So in this case, right compound two would exhibit dile dile interactions because there's a difference in electron negativity between carbon and nitrogen. There is in fact going to be a dipole moment and therefore a polar covalent bond. So because dile dile interactions are weaker than hydrogen bonds, compound two is going to have the lowest boiling point. So now let's compare the hydrogen bonds of an amine as opposed to an alcohol. No recall that the strength of a hydrogen bond increases as the electron negativity of the atom hydrogen is attached to increases. So recall that oxygen is more electron negative than nitrogen. So what that means is that hydrogen bonds formed by alcohols are stronger than hydrogen bonds formed by amines. So even though compounds one in three, both exhibit bonding right compound one would have slightly weaker h bonds because nitrogen is less electron than oxygen. So if we're ranking these molecules from highest to lowest boiling point compound three would have the highest boiling point followed by compound one and then compound two. And so if I scroll down here to consider my answer choices, the correct answer is going to be option a in the multiple choice because in order of decreasing boiling point, it would be compound three followed by one, followed by two. And so molecule two has the higher boiling point than molecule one because molecule one forms stronger hydrogen bonds. Molecule two has the lowest boiling because it exhibits the weaker dipole forces and there you have it. So with that being said, thank you so very much for watching and I hope you found this helpful.

Arrange the following compounds in order of increasing boiling point. Explain why you placed them in that order.
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Verified Solution

Key Concepts

Boiling Point

Intermolecular Forces

Molecular Structure