Hi Natasha,

1. How can toluene hydrogen bond as the answer says? Isn't it made of only carbons and hydrogens?

Toluene doesn't hydrogen bond - the reasoning the answer key provides here is wrong. However because it is aromatic, it has significant amounts of pi stacking, and has stronger intermolecular forces than one would expect for such a non polar molecule. As a result, it has a pretty high boiling point, and requires a lot of energy to vaporize.

It's possible they're trying to say that the aromatic C-H have more depolarized Hs and thus can hydrogen bond, but I wouldn't really describe this in this way.

2. Why wouldn't the molecule with the lowest boiling point and highest vapour pressure (diethyl ether) require the least energy to overcome intermolecular forces? Isn't that what boiling point indicates?

Yeah, I don't think this question is correct. If you were asked to predict from intermolecular forces alone, you would put hexane as lower boiling than diethyl ether because it has only van der waals forces, while diethyl ether has some dipole/dipole forces.

However it seems that the molecular size and high surface area of hexane trumps the dipole moment of ether (which tends to be quite small because it symmetrically cancels), as you see from the boiling points. And it's even weirder because the question specifically asks you to look at Table 1, where it shows the bp of diethyl ether is lower than that of n-hexane.

As a result, consider reporting this as a Typo to Altius so that they can rectify this question.

I hope this helps, and good catch!

Katt