AAMC - THF & Toluene question

[TTSD]

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On 6R I think.. it asked about the differences between THF and Toluene in one of its passages. The answer was that THF I think can hydrogen bond while the other can't (might be the other way, but I can't access the questions from this computer).

But doesn't THF have an ether.. and according to my Kaplan book Ether's can't hydrogen bond? Is the Kaplan book wrong?

 

[maygirl]

I think they mean that THF can hydrogen bond with water (it can be a hydrogen bond acceptor, but not a donor). Perhaps the question asks whether it can at least participate in H-bonding. You're right about it not being able to hydrogen bond with other THF molecules.

Good luck! (My brain is currently fried, so I don't really know whether this is correct)

 

[peterockduke]

the last post is correct

 

[indo]

didn't it ask which one has a higher or lower boiling point? I think the answers mentioned the h bonding.

 

[Mudd]

Originally posted by TTSD
But doesn't THF have an ether.. and according to my Kaplan book Ether's can't hydrogen bond? Is the Kaplan book wrong?

It's not that your Kaplan book is wrong persay, it's that they don't elaborate enough to cover this question. In an attempt to oversimplify, they have omitted a key point. Ethers cannot form H-bonds with themselves. They have a lone pair donor in oxygen, but all of the hydrogens on an ether are bonded to carbon, so their partial positive charge is too small to form an interaction with oxygen.

However, the oxygen in an ether can donate its lone pair of electrons to a protic hydrogen on another molecule, such as water.

The exact question (#60 on AAMC 5) is:

• 
  Which of the two solvents in Figure 1 is most soluble in H2O?

The best answer is THF, because it can form H-bonds with water while toluene (having no lone pairs) cannot.

Moral to story: Many MCAT prep books give the bare minimal, and the MCAT loves to make you think outside the box. Know the basics, but be willing to think beyond the flashcards.