hydrogen bonding with ions?

[yoyohomieg5432]

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this question is from AAMC 10. when i think if hydrogen bonding i always think between O, N, and F. Partial charges form, thus allowing them to come together.

In this question though, it's bonding between OH and an O-. This is still considered hydrogen bonding? I guess I never really considered the case where one element is negatively charged.

In the same manner, when you put HCL into water and it forms H+ and Cl-, the Cl and water interacting is also considered H bonding?

 

[Synapsis]

this question is from AAMC 10. when i think if hydrogen bonding i always think between O, N, and F. Partial charges form, thus allowing them to come together.

In this question though, it's bonding between OH and an O-. This is still considered hydrogen bonding? I guess I never really considered the case where one element is negatively charged.

In the same manner, when you put HCL into water and it forms H+ and Cl-, the Cl and water interacting is also considered H bonding?

I would say it is. Hydrogen bonding is just a dipole-dipole interaction. Between OH and O-, each of those has a dipole, even though that minus is there. The fact that the minus is there just makes it a stronger dipole (as opposed to a partially negative oxygen, like in a carbonyl).

The second case doesn't necessarily count as hydrogen bonding, at least the way most books define it. The actual definition involves a highly electronegative atom and hydrogen, but my textbooks and all review books say that it's restricted only to F, O, or N.

 

[yoyohomieg5432]

I would say it is. Hydrogen bonding is just a dipole-dipole interaction. Between OH and O-, each of those has a dipole, even though that minus is there. The fact that the minus is there just makes it a stronger dipole (as opposed to a partially negative oxygen, like in a carbonyl).

The second case doesn't necessarily count as hydrogen bonding, at least the way most books define it. The actual definition involves a highly electronegative atom and hydrogen, but my textbooks and all review books say that it's restricted only to F, O, or N.

So what's the difference between a dipole dipole and H bond? Both are dipole interactions. Is H bond just stronger dipole dipole? (and the obvious that it must involve F/O/N)

Also, this is what i gleaned from a wiki article on solvation:
Solvation involves different types of intermolecular interactions: hydrogen bonding, ion-dipole, and dipole-dipole attractions or van der Waals forces. The hydrogen bonding, ion-dipole, and dipole-dipole interactions occur only in polar solvents.

Is hydrogen bonding only involved if the solute is capable of H bonding? I.e. H20 and an alcohol. But H20 and Cl- isn't H bonding? even though H20 is still donating a partial positive H?

 

[adrakdavra]

this is a real popular MCAT Q, The idea here is that the OH and O- are both in the axial position, therefore, they can make H-bonds.
H is bonding to FON is inter molecular H-bonding. H CL with another H CL is dipole dipole .
H-bonds are not a full charged, only ionic bonds are full charges and a lot stronger then H- bonding.

Again the idea here is a bout the axial vs equilateral potion
Axial will make H bonds
Equilateral will not

 

[Synapsis]

So what's the difference between a dipole dipole and H bond? Both are dipole interactions. Is H bond just stronger dipole dipole? (and the obvious that it must involve F/O/N)

Also, this is what i gleaned from a wiki article on solvation:
Solvation involves different types of intermolecular interactions: hydrogen bonding, ion-dipole, and dipole-dipole attractions or van der Waals forces. The hydrogen bonding, ion-dipole, and dipole-dipole interactions occur only in polar solvents.

Is hydrogen bonding only involved if the solute is capable of H bonding? I.e. H20 and an alcohol. But H20 and Cl- isn't H bonding? even though H20 is still donating a partial positive H?

That just it, there's no difference between hydrogen bonding and dipole-dipole interactions. Hydrogen bonding is just the strongest type of dipole-dipole interaction there is. But they're still the same thing. For an example of a dipole-dipole interaction that's not hydrogen bonding, check out acetone.

All the molecules have dipoles interacting, but no H's for H-bonding.

The interaction with Cl-, solvation, is just the interaction between chloride's negative charge with the partial positive of hydrogen. That's because you can't just have a charge in solution without a counterion. That happens with any negative (and positive charge) in solution. If you put potassium hydroxide in solution, K+ interacts with the partial negative oxygen. The K+ is solvated.

 

[QrtrLifeCrisis]

It is bizarre that they called that H-bonding. The definition for H-bonding is usually restricted to the FON atoms and involves uncharged species.

What they depicted is probably more accurately termed an ion-dipole interaction, which is stronger than typical H-bonding.

 

[sakabato93]

Anions undergoing solvation when dissolved in water DO undergo hydrogen bonding with the hydrogen atoms of water molecules. Its just a special definition that's not seen very often.


Cations undergoing solvation when dissolved in water dissolve under a different mechanism that involves interaction with the lone pairs on oxygen atoms of water molecules (formation of dative/coordinate covalent bonds).

Here is a good site to reference: http://www.chemguide.co.uk/atoms/bonding/hbond.html

 

[Synapsis]

Anions undergoing solvation when dissolved in water DO undergo hydrogen bonding with the hydrogen atoms of water molecules. Its just a special definition that's not seen very often.


Cations undergoing solvation when dissolved in water dissolve under a different mechanism that involves interaction with the lone pairs on oxygen atoms of water molecules (formation of dative/coordinate covalent bonds).

Here is a good site to reference: http://www.chemguide.co.uk/atoms/bonding/hbond.html

That's interesting - never heard of it. Sounds right, but it might be better to stick with the basic FON rule if they ask something about H-bonding.

Unless they ask about this specific type of case, which would be a stretch (right?).

 

[sakabato93]

That's interesting - never heard of it. Sounds right, but it might be better to stick with the basic FON rule if they ask something about H-bonding.

Unless they ask about this specific type of case, which would be a stretch (right?).

Agreed. For the purposes of the MCAT, the FON rule should be sufficient. I'd imagine that this criterion for hydrogen bonding isn't very useful outside of chemistry majors.


Good luck with studying!