Hydrogen Bonding / Carbonyl oxygen

[Samchik]

In TPR review book on page 583, they say that:

Acetic acid has one hydrogen-bond donor and one hydrogen-bond acceptor.
At the same time, 1,2-ethanediol has 2 hydrogen-bond donors and 2 hydrogen-bond acceptors.

Shouldn`t it be one hydrogen-bond donor and two hydrogen-bond acceptors in acetic acid? OH group = 1 h.b. donor and at the same time acceptor, and carbonyl`s oxygen lone pairs can be h.b. acceptors.

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[Kimchii]

No because the OH on acetic acid isnt an H bond its a covalent bond. If acetic acid dissociates and becomes O- then it wouldnt accept an H as an H bond but as a covalent bond.

 

[Samchik]

Thank you, I think it just depends on the functional group and the molecule under question. For example, acetic acid forms dimers due to hydrogen bonding upon crystallization. And water and alcohol can use their -OH group as hydrogen bond donor and acceptor at the same time, whereas carboxylic acids can`t use their -OH group as hydrogen bond acceptor.

 

[mikexima]

I understand it the way OP said it. not sure what covalent bond has to do with it? H on F O N = hydrogen bonding. C=O accepts a hydrogen bond but cant donate. O-H does both.

 

[tendiw]

Yes there are two acceptors and one donor. There must be a typo in your study material.

 

[geeyouknit]

In TPR review book on page 583, they say that:

Acetic acid has one hydrogen-bond donor and one hydrogen-bond acceptor.
At the same time, 1,2-ethanediol has 2 hydrogen-bond donors and 2 hydrogen-bond acceptors.

Shouldn`t it be one hydrogen-bond donor and two hydrogen-bond acceptors in acetic acid? OH group = 1 h.b. donor and at the same time acceptor, and carbonyl`s oxygen lone pairs can be h.b. acceptors.

It sounds like there's a confusion of definition?

Hydrogen bonds are intermolecular bonds created when there are intramolecular bonds (ie, Covalent) between H atom and N,O,F atoms.
The acetic acid has 1 OH group that creates a 1 HB donor (H), and one HB acceptor (O). The carbonyl Oxygen is attached covalently to the carbon. The diff in eneg isn't great enough as a H-O covalent bond to be as strong as a H-bond.

The donors are the H atoms in an atom. The acceptors are the NOF atom that's connected to an H atom.

 

[Samchik]

It sounds like there's a confusion of definition?

Hydrogen bonds are intermolecular bonds created when there are intramolecular bonds (ie, Covalent) between H atom and N,O,F atoms.
The acetic acid has 1 OH group that creates a 1 HB donor (H), and one HB acceptor (O). The carbonyl Oxygen is attached covalently to the carbon. The diff in eneg isn't great enough as a H-O covalent bond to be as strong as a H-bond.

The donors are the H atoms in an atom. The acceptors are the NOF atom that's connected to an H atom.

I understood the definition, I just can`t understand why TPR science book says that acetic acid has only one hydrogen-bond donor and one hydrogen-bond acceptor. Probably it`s just a typo in the book.

 

[tendiw]

Lol that's what I said haha. You can look through the errata list for TPR. I'm sure it's in there.

 

[mikexima]

TPR is 100% wrong.

I can confirm this for you because I remember on one of the AAMC tests a question asked about boiling point being higher between carboxylic acid and alcohol, the answer was the acid !

 

[Samchik]

TPR is 100% wrong.

I can confirm this for you because I remember on one of the AAMC tests a question asked about boiling point being higher between carboxylic acid and alcohol, the answer was the acid !

This was the question for the 3 compounds on that page:

Example 1-14: Rank the following three compounds in order of increasing boiling point:

Hydrogen-bonding affects boiling point, so in this case alcohol (1,2-ethanediol) will have the highest BP because it has 2 h. bond donors and 2 h. bond acceptors; diethyl ether will have the lowest BP because it can`t form hydrogen bonds (with itself) because it has only hydrogen bond acceptor. And the acetic acid will be in between. You should be careful with boiling points of acids and alcohols because besides hydrogen bonding other interactions come into play as is in this case. Alcohol in this problem has higher BP than acid.

 

[Samchik]

Lol that's what I said haha. You can look through the errata list for TPR. I'm sure it's in there.

Do you know where I can find TPR`s errata list?