Aamc 9 # 7 (ps)

[eldoctor]

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The question asks what type of intermolecular interaction can EtOH undergo with water that MTBE (C4H9OCH3, an ether) can NOT?

The answer is Hydrogen bonding. I thought H-bonds CAN be formed inTERmolecularly with water for both compounds since water donates the H to MTBE, but MTBE cannot form INTRAmolecular H bonds.

Any ideas?

 

[Rabolisk]

Bad question, but it's still the best wrong answer.

 

[chemtopper]

In MTBE,there is oxygen which is not so exposed due to bulky nature of the tert-butyl group.This Oxygen is not available for H - bonding with water .
May be that can be the reason.

 

[golgiapparatus88]

The question asks what type of intermolecular interaction can EtOH undergo with water that MTBE (C4H9OCH3, an ether) can NOT?

The answer is Hydrogen bonding. I thought H-bonds CAN be formed inTERmolecularly with water for both compounds since water donates the H to MTBE, but MTBE cannot form INTRAmolecular H bonds.

Any ideas?

To get the idea of hydrogen bonding, draw out two water molecules and draw the dotted lines showing where they hydrogen bond. You have the partial positive Hydrogen atom that hydrogen bonds with an partially negative charged oxygen, and the reverse is true for oxygen binding with hydrogen.

The same thing occurs in EtOH. The most important thing to notice is that there is a hydrogen bonded directly to the oxygen atom. Methyl hydrogens DO NOT undergo hydrogen bonding because Carbon is not electronegative enough.

MTBE is a ether, R-O-R. Going back and comparing to the the water or EtOH example, we see that both R groups are methyl groups. No hydrogen bonding occurs!

On a side note, the oxygen does have 2 lone pairs so it is a Lewis Base (electrophile)

 

[Rabolisk]

To get the idea of hydrogen bonding, draw out two water molecules and draw the dotted lines showing where they hydrogen bond. You have the partial positive Hydrogen atom that hydrogen bonds with an partially negative charged oxygen, and the reverse is true for oxygen binding with hydrogen.

The same thing occurs in EtOH. The most important thing to notice is that there is a hydrogen bonded directly to the oxygen atom. Methyl hydrogens DO NOT undergo hydrogen bonding because Carbon is not electronegative enough.

MTBE is a ether, R-O-R. Going back and comparing to the the water or EtOH example, we see that both R groups are methyl groups. No hydrogen bonding occurs!

On a side note, the oxygen does have 2 lone pairs so it is a Lewis Base (electrophile)

Ethers, at least small ethers can accept hydrogen bonds.

 

[web2linc]

Ethers are polar, which makes them a good solvent. However, they don't hydrogen bond with each other. EtOH do hydrogen bond with each other.



Ether - R-O-R' <-- Ether molecules cannot form hydrogen bonds amongst each other, resulting in a relatively low boiling point compared to that of the analogous alcohols.

Alcohol - R-O-H <-- Can participate in intermolecular hydrogen bonding.

 

[Rabolisk]

Ethers are polar, which makes them a good solvent. However, they don't hydrogen bond with each other. EtOH do hydrogen bond with each other.



Ether - R-O-R' <-- Ether molecules cannot form hydrogen bonds amongst each other, resulting in a relatively low boiling point compared to that of the analogous alcohols.

Alcohol - R-O-H <-- Can participate in intermolecular hydrogen bonding.

True, but not what the question is asking.

 

[MM88]

In MTBE,there is oxygen which is not so exposed due to bulky nature of the tert-butyl group.This Oxygen is not available for H - bonding with water .
May be that can be the reason.

That's the most logical reason. If stearic hindrance prevents stronger, potentially (I say that because they CAN'T form) polar covalent bonds from forming, I'm sure they would have the same effect on weaker van de waals forces like H-bonding.

 

[squirrelsrock]

1) the question asks if mtbe can hydrogen bond with water, not with itself. So it doesn't matter that it doesn't have a partially positive to donate. It can use the lone pairs on the Oxygen to attract two partially positive hydrogens from water and hydorgen bond.

2) The fact that it is bulky could affect hydrogen bonding, but diethyl ether hydrogen bonds with water and it's just as, if not a little less bulky, than mtbe.


None of the answer choices answer the question.http://img2.studentdoctor.net/images/smilies/mad.gif