Destroyer OC #14, page 10

[qkchen]

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hi guys,

for question 14, i am wondering why choice e (t-butoxide) would not have the highest boiling point. this is an anion, and could form ion-dipole interactions, which are technically stronger intermolecular forces than H-bonds, which should make it have the strongest intermolecular forces. (there are also branching in this t-butoxide which may lower boiling point slightly). (or are we to assume that these are not dissolved in water so my reasoning would not apply).

that was a mouthful. any insights greatly appreciated.

 

[invictusx]

hi guys,

for question 14, i am wondering why choice e (t-butoxide) would not have the highest boiling point. this is an anion, and could form ion-dipole interactions, which are technically stronger intermolecular forces than H-bonds, which should make it have the strongest intermolecular forces. (there are also branching in this t-butoxide which may lower boiling point slightly). (or are we to assume that these are not dissolved in water so my reasoning would not apply).

that was a mouthful. any insights greatly appreciated.

I don't have the 2011 version so you would have to provide other choices. I don't think you're supposed to assume it's dissolved in water. The highest boiling points would be those with hydrogen bonding activity, especially carboxylic acids. Carboxylic acids are probably better than t-butoxide because of how of the level of hydrogen bonding capability of carboxylic acids. Branching plays a big role in determining BP because of van der Waals forces (I'm sure you know the reason for this so I'm not going to explain it).

Also, as t-butoxide, you don't really "form" hydrogen bonds, you make them. Hydrogen bonds are attractive "interactions". Just because t-butoxide is highly anionic, it doesn't mean that it can't form other molecules, like ethers, which have lower BP than esters and carboxylic acids.

Does that make any sense? Let me know

 

[qkchen]

hi invictusx,

the other choices were two ethers, 2-pentanol, 2,2-dimethyl-1-propanol and t-butoxide. the correct answer was 2-pentanol.

i see where you're coming from. i know that H-bonding will raise boiling (and melting) points, whereas branching will decrease them. however, where i got caught up is when they presented the salt, t-butoxide. if this were to be dissolved in water, the ion-dipole interactions would be stronger than the H-bonds (Chad's videos), meaning they would have the stronger intermolecular forces, and consequently, higher boiling point.

anyways, i guess i overanalyzed it by assuming these were dissolved in solution.

I don't have the 2011 version so you would have to provide other choices. I don't think you're supposed to assume it's dissolved in water. The highest boiling points would be those with hydrogen bonding activity, especially carboxylic acids. Carboxylic acids are probably better than t-butoxide because of how of the level of hydrogen bonding capability of carboxylic acids. Branching plays a big role in determining BP because of van der Waals forces (I'm sure you know the reason for this so I'm not going to explain it).

Also, as t-butoxide, you don't really "form" hydrogen bonds, you make them. Hydrogen bonds are attractive "interactions". Just because t-butoxide is highly anionic, it doesn't mean that it can't form other molecules, like ethers, which have lower BP than esters and carboxylic acids.

Does that make any sense? Let me know

 

[invictusx]

hi invictusx,

the other choices were two ethers, 2-pentanol, 2,2-dimethyl-1-propanol and t-butoxide.

i see where you're coming from. i know that H-bonding will raise boiling (and melting) points, whereas branching will decrease them. however, where i got caught up is when they presented the salt, t-butoxide. if this were to be dissolved in water, the ion-dipole interactions would be stronger than the H-bonds (Chad's videos), meaning they would have the stronger intermolecular forces, and consequently, higher boiling point.

anyways, i guess i overanalyzed it by assuming these were dissolved in solution.

Yeah, only if it were dissolved in water would the ion-dipole interactions be stronger, otherwise nope! Don't forget, this is orgo, not genchem and that often trips people up. I've never tried Chad so I don't know how effective he is.

 

[wall1two]

that molecule is not tertbutoxide anion, it is an ester. otherwise you are 100% correct, it is a methyl group hanging onto that bad boy not a charge

 

[qkchen]

nice catch, being an ether makes it a whole different question