Question

The boiling point of butane, acetone, and propanol are 0 *C, 56*C, and 97*C respectively. These molecules, shown below, have about the same number of atoms, electrons, and molar masses, yet their boiling points are quite different, Identitify the dominant noncovalent interaction present for each of these molecules and explain, in terms of these interactions, why the boiling points are so different?

Answer 1

For butane: The dominant IMF of butane is LDF because carbon and hydrogen have about the same EN, therefore resulting in a weak bond force means molecules of butane will boil at lower temperatures.

Answer 2

For acetone: acetone IMF is dipole-dipole because oxygen has a higher EN than carbon. Because dipole-dipole IMF is stronger and the EN are different the boiling point is higher.

Answer 3

dipole dipole is stronger than LDF

Answer 4

@Photon336

Answer 5

For propanol: The dominant IMF in propanol is HB because we have an o-H, a hydrogen and oxygen linked together. It takes a great amount of energy to break these bonds so BP must be high.

Answer 6

@Empty

Answer 7

I'm not sure what you mean in your answers, partially because you use too many abbreviations I'm unfamiliar with, IMF could mean Intramolecular Force or Intermolecular Force idk? Two very different things.

So here seems like a good place to start, when you say:
"For propanol: The dominant IMF in propanol is HB because we have an o-H, a hydrogen and oxygen linked together. It takes a great amount of energy to break these bonds so BP must be high."

Describe this O-H bond more. Is this between two separate molecules or the same molecule?

Answer 8

I mean intermolecular force. Let me think about your question some more

Answer 9

Yeah sure, I might be a little preoccupied so if I don't respond right away don't worry I just got back from sailing and I'm hungry lol.

Answer 10

The O-H is within one molecule. I am talking about the hydrogen bonds in each molecule of in itself. Sailing? Nice!

Answer 11

Ah ok, then breaking that O-H bond in particular doesn't contribute towards turning it from liquid to gas, that will specifically deprotonate a single molecule. What you want to do is separate molecules apart from each other, so you need to be breaking this kinda O-H bond:

The reason being, to go from liquid to gas phase, you are really overcoming this intermolecular force so that the molecules are independently bouncing around in space. This is specifically a hydrogen bond, and it's basically the strongest dipole-dipole interaction, but it's exceptionally strong that it's sorta almost a covalent bond.