H-bonding in ketones/aldehydes

[TXKnight]

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this should be an easy one:
I know aldehydes and ketones cannot H bond in aqueous solutions, but why?
is it because the carbonyl oxygen is the H bond donor but it lacks a hydrogen that could act as the H bond acceptor?
I am confused by what I've found online and by the mantra,you know, H,F,O,N?
Anyone? thank you!

 

[Ssina]

they can H- bond with water molecules in the aqueous solution, they just can't H- bonds with themselves (or if the solution doesn't have the H donating group)

Hence why solution of only ketone/ald has low bp vs. water

 

[Pisiform]

this should be an easy one:
I know aldehydes and ketones cannot H bond in aqueous solutions, but why?
is it because the carbonyl oxygen is the H bond donor but it lacks a hydrogen that could act as the H bond acceptor?
I am confused by what I've found online and by the mantra,you know, H,F,O,N?
Anyone? thank you!

Yes, partly.

From what I have read, hydrogen bonding occurs only when we have an electronegative atom present (F,O,Cl,N) and that electronegative atom should have Lone pair of electron + hydrogen atom attached.

Like in alcohol, Oxygen is electronegative atom and has 2 pairs of lone electron + a hydrogen attached. So, it can form H2 bond.

Where as in Keton, Aldehyde - they only have Oxygen and lone pairs but no Hydrogen attached.

 

[Ssina]

Cl doesn't actually count, it's only F,O,N as the electroneg groups with hydrogen, at least from what I have read

 

[TXKnight]

they can H- bond with water molecules in the aqueous solution, they just can't H- bonds with themselves (or if the solution doesn't have the H donating group)

Hence why solution of only ketone/ald has low bp vs. water

ok, so its with themselves they can't H-bond (I can clearly see why not) but they CAN in aq. solutions regardless of their lack of hydrogen, (only O does the trick) right?

 

[Ssina]

Yeah exactly, it just needs the lone pair from oxygen of the carbonyl group with H of the water.... You don't need a H group attached to them, like carboxylic acids where u get H- bonding with the carbonyl group and the alcohol group

 

[TXKnight]

Yeah exactly, it just needs the lone pair from oxygen of the carbonyl group with H of the water.... You don't need a H group attached to them, like carboxylic acids where u get H- bonding with the carbonyl group and the alcohol group

Perfect...thank you!

 

[TXKnight]

Yes, partly.

From what I have read, hydrogen bonding occurs only when we have an electronegative atom present (F,O,Cl,N) and that electronegative atom should have Lone pair of electron + hydrogen atom attached.

Like in alcohol, Oxygen is electronegative atom and has 2 pairs of lone electron + a hydrogen attached. So, it can form H2 bond.

Where as in Keton, Aldehyde - they only have Oxygen and lone pairs but no Hydrogen attached.

..Thank you, yeah I was also kind of confused by this, for instance, throw in the definition of aprotic solvent (think acetone) and it gets a little misleading.
Acetone cannot H-bond with itself (it abviously lacks H) but, by the rationale that it only needs to bond to a hydrogen elsewhere to make it an H-bond then we might as well call acetone protic.... The example is that we have one person saying that it suffices having only the F,O,N bonded to an H and we also have another one saying that you need both molecules have a H - F/O/N. wtf?

 

[Ssina]

loool for H-bonding you need a lone pair of F,O,N and the H bonded to F,O,N ( I am sure you know this part, but just in case my reply was obscure)

F/O/N: .... H-F/O/N

that's why I was saying when you put acetone, ketone, or aldehyde in water (in an aqueous solution) the carbonyl O will hydrogen bond to the H of water only... but when we are talking about protic vs. aprotic solvents... I see it from the perspective of the H, so water has an H to donate for intermolecular forces of whatever we are stabilizing in a reaction (e.g. an intermediate of E1 reaction), while aprotic doesn't have the H to give, like acetone!

 

[TXKnight]

👍

loool for H-bonding you need a lone pair of F,O,N and the H bonded to F,O,N ( I am sure you know this part, but just in case my reply was obscure)

F/O/N: .... H-F/O/N

that's why I was saying when you put acetone, ketone, or aldehyde in water (in an aqueous solution) the carbonyl O will hydrogen bond to the H of water only... but when we are talking about protic vs. aprotic solvents... I see it from the perspective of the H, so water has an H to donate for intermolecular forces of whatever we are stabilizing in a reaction (e.g. an intermediate of E1 reaction), while aprotic doesn't have the H to give, like acetone!

 

[Erythropoietin]

loool for H-bonding you need a lone pair of F,O,N and the H bonded to F,O,N ( I am sure you know this part, but just in case my reply was obscure)

F/O/N: .... H-F/O/N

that's why I was saying when you put acetone, ketone, or aldehyde in water (in an aqueous solution) the carbonyl O will hydrogen bond to the H of water only... but when we are talking about protic vs. aprotic solvents... I see it from the perspective of the H, so water has an H to donate for intermolecular forces of whatever we are stabilizing in a reaction (e.g. an intermediate of E1 reaction), while aprotic doesn't have the H to give, like acetone!

The bolded part is important because in the first case, you need a lone pair OF one of the FON elements, which can bond to an H already bonded to another FON ...I guess I said the same thing 😀