Why can't pyruvate hydrogen bond, as opposed to lactate, which can?

[ydolem89]

I'm interested in understanding the details. I thought that H-bond could occur between a compound with H-(O,N or F) and a compound with very electronegative atom (O,N or F). For example, I know that ether (Me-O-Me) can hydrogen bond to compounds with H-(O, F or N) but can't hydrogen bond to itself. I can understand why pyruvate can't H-bond with itself, but why not with other compounds with H-(O,N or F)?

I was thinking that maybe it was because lactate had a small dipole at the secondary alcohol between O and H, and that pyruvate didn't have that...but I honestly don't really know.

Thanks so much in advance!!

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[Ssina]

wait so where did you read the fact that pyruvate can't hydrogen bond with itself or other H-(F,O,N)?!
I can see how with certain pH it will deprotonated so no H to H-bond with itself, but the Os are free to H-bond with let say water!?

 

[ydolem89]

wait so where did you read the fact that pyruvate can't hydrogen bond with itself or other H-(F,O,N)?!
I can see how with certain pH it will deprotonated so no H to H-bond with itself, but the Os are free to H-bond with let say water!?

It was detailed in an explanation in the ExamKracker's Orgo book. The original question asked which compound would have the higher boiling point. The back of the book explained that "lactate can form hydrogen bonds, which increase bp". So I interpreted this as pyruvate not being able to from hydrogen bonds, which confused me, because I thought that it could...

 

[Ssina]

It was detailed in an explanation in the ExamKracker's Orgo book. The original question asked which compound would have the higher boiling point. The back of the book explained that "lactate can form hydrogen bonds, which increase bp". So I interpreted this as pyruvate not being able to from hydrogen bonds, which confused me, because I thought that it could...

maybe just the fact that lactate will be able to H-bond more then it has a higher bp vs. pyruvate... since lactic acid has an -OH group instead of a keton, the O has 2 lone pairs to H-bond and also it has an H that another O can H-bond to vs. the keton that only has the O with 2 lone paire!

It could be wrong reasoning for it, but I would pick lactic acid just for that!

 

[Jepstein30]

Well thats the point. Pyruvate can't H-bond with itself, as you said in the first post. This is because it doesn't have an H-bond donor.

You are boiling pyruvate, there's nothing else in the system. Pyruvate can't form H-bonds with itself so there will be no self-association. Lactate, with both an H-bond donor and acceptor, can H-bond with itself so lactate molecules will self associate, leading to a higher BP.

You have the right approach but are going too far in your analysis!!

 

[ydolem89]

Thanks for the replies, everyone!

To further clarify, I guess I'm wondering if pyruvate can H bond AT ALL. For example, with water.

Thank you!!

 

[theseeker4]

Thanks for the replies, everyone!

To further clarify, I guess I'm wondering if pyruvate can H bond AT ALL. For example, with water.

Thank you!!

Yes, it can bond to a compound with a H-(O, F, N), but not to any compound with no hydrogen available for the hydrogen bond.

 

[ydolem89]

Yes, it can bond to a compound with a H-(O, F, N), but not to any compound with no hydrogen available for the hydrogen bond.

Thank you! This has been bugging me for days. I was freaking out because the concept of H bonding is so elementary and I thought I'd had it wrong for all these years!