Probably A Simple Organic Question

[MedPR]

So alcohols are more acidic than amines, which means that alcohols are better proton donors, primarily because Oxygen is larger and more polarizing than Nitrogen. Alcohols also have a higher boiling point than Amines, due to the stronger Hydrogen bonds.

I understand those two concepts separately, but if strength of acidity is defined by dissociation in aqueous solution, wouldn't a stronger acid need to have a weaker hydrogen bond, thus making it easier for a base to abstract the proton? TBR says that hydrogen bonding in Alcohols is stronger than in Amines. I'm not saying TBR is wrong, I know my question stems from holes and discontinuity in my understanding.

I'm going to attempt to answer my own question, and I would appreciate it if you guys could let me know if I'm on the right track.

The OH bond in individual alcohol compounds is weaker than the NH bond in individual amines due to polarizability and electron withdraw, thus making Alcohols more acidic than NH. But when you have a bunch of Alcohols H-bonding to each other, those interactions are stronger than a bunch of Amines H-bonding to each other, thus making the boiling point higher for Alcohols than Amines.

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[chiddler]

If a given alcohol is more acidic, then the O-H bond is weaker. This also means that the electron cloud is closer to oxygen which means a stronger partial negative charge and therefore stronger hydrogen bonds.

I think if the hydrogen can stay bound to the ion, then it will exhibit very strong hydrogen bond interactions because of the reason I mention.

 

[ljc]

My understanding (correct me if I'm wrong): Be careful you don't mix up the O-H bond with "hydrogen bond". One is intermolecular, one is intramolecular. Hydrogen bonds hold two separate molecules together, while the O-H bond is more ionic in nature, as it holds two atoms within a molecule together.

 

[MedPR]

If a given alcohol is more acidic, then the O-H bond is weaker. This also means that the electron cloud is closer to oxygen which means a stronger partial negative charge and therefore stronger hydrogen bonds.

I think if the hydrogen can stay bound to the ion, then it will exhibit very strong hydrogen bond interactions because of the reason I mention.

I think you're right, except that when comparing atoms in the same row, the electronegativity is more important than the atomic radius, since the difference between the atomic radii of N and O are negligible. Unless by "electron cloud" you mean electron density! Then yes, I agree.

Same row = electronegativity
Same column = atomic radius

My understanding (correct me if I'm wrong): Be careful you don't mix up the O-H bond with "hydrogen bond". One is intermolecular, one is intramolecular. Hydrogen bonds hold two separate molecules together, while the O-H bond is more ionic in nature, as it holds two atoms within a molecule together.

Yea, that's what I was trying to say in the OP. I just wanted to make sure I was understanding it correctly. Thanks 🙂

The OH bond in individual alcohol compounds is weaker than the NH bond in individual amines due to polarizability and electron withdraw, thus making Alcohols more acidic than NH. But when you have a bunch of Alcohols H-bonding to each other, those interactions are stronger than a bunch of Amines H-bonding to each other, thus making the boiling point higher for Alcohols than Amines.

Thank you both for your input 👍

 

[ilovemedi]

Okay, I'm still confused about amines vs. alcohol. on page 46 it says that "amine lone pair binds the protic alcohol more tight than an alochol lp binds the protic H of amine". I get this--nitrogen is more basic and wants to hold onto the hydrogen tighter.

then the next couple of pages (48) says that alcohol hydrogen bonds (with each other) are stronger than amines bonding with each other.. I thought we just established that amines bond tighter to hydrogens than alcohols do (and are hence strongest).

 

[MedPR]

Okay, I'm still confused about amines vs. alcohol. on page 46 it says that "amine lone pair binds the protic alcohol more tight than an alochol lp binds the protic H of amine". I get this--nitrogen is more basic and wants to hold onto the hydrogen tighter.

then the next couple of pages (48) says that alcohol hydrogen bonds (with each other) are stronger than amines bonding with each other.. I thought we just established that amines bond tighter to hydrogens than alcohols do (and are hence strongest).

Your first paragraph is talking about covalent bonds. So the covalent bond between the nitrogen and one hydrogen in NH3 is stronger than the covalent bond between an the oxygen and hydrogen in an alcohol. You can also think of it as the Oxygen is more electronegative, so it is going to want the Hydrogen's electron all for itself; Oxygen doesn't want to share electrons in a bond.

Your second paragraph is talking about Hydrogen bonds between different molecules. If you place aqueous amine and aqueous alcohol in two different flasks, the alcohol flask will have stronger interactions (H-bonding) between individual molecules compared to the amine flask.

Stronger hydrogen bond = weaker covalent bond. So in CH3OH, the O-H bond is weakened by the hydrogen bond with another CH3OH.

 

[ilovemedi]

Your first paragraph is talking about covalent bonds. So the covalent bond between the nitrogen and one hydrogen in NH3 is stronger than the covalent bond between an the oxygen and hydrogen in an alcohol. You can also think of it as the Oxygen is more electronegative, so it is going to want the Hydrogen's electron all for itself; Oxygen doesn't want to share electrons in a bond.
.

I thought it was talking about hydrogen bonds. page 48 - before the sentence it says 'You should be aware that not all hydrogen bonds have the same strength.' Aditionally, page 48 says that the strongest hydrogen bond is with a lone pair from nitrogen..

I think I kinda of get it.. the reason why alcohols have stronger hydrogen bonding is because the oxygen has 2 lone pairs and can H-bond more when, as you said, there are NUMEROUS molecules.

 

[MedPR]

I thought it was talking about hydrogen bonds. page 48 - before the sentence it says 'You should be aware that not all hydrogen bonds have the same strength.' Aditionally, page 48 says that the strongest hydrogen bond is with a lone pair from nitrogen..

I think I kinda of get it.. the reason why alcohols have stronger hydrogen bonding is because the oxygen has 2 lone pairs and can H-bond more when, as you said, there are NUMEROUS molecules.

Yea you're right, both paragraphs were talking about H-bonding. I misread your first paragraph and thought you were talking about what I explained in my first paragraph.


H-bonding between alcohols is stronger than h-bonding between amines. But yes, in h-bonding between an amine and an alcohol, the amine bonds more strongly to the protic H in O-H than the alcohol does to the amine H because, as you said, the amine is more basic and accepts the protic H better than the alcohol does.

Your second paragraph was talking about intermolecular forces (H-bonding) between multiple alcohols compared to intermolecular forces between multiple amines.

 

[ilovemedi]

thanks for clarifying.. i think i get it.. a simple concept turned out to be confusing because of the wording.. sigh.

 

[MedPR]

thanks for clarifying.. i think i get it.. a simple concept turned out to be confusing because of the wording.. sigh.

As long as you get it 🙂