Polarity: ion vs. hydrogen bonding molecule

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regeneration

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Does being an ion make a molecule more polar (say w/ 1. polar protic solvent and 2.polar aprotic solvent) than being able to hydrogen bond? For example, an O- substituent vs. an alcohol substituent, or NR4+ vs. NR2- vs. NHR3.

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Typically that will be the case (being an ion is more polar), but polarity of a molecule has nothing to do with solvent - although the polarity may change how it interacts with the solvent.

In your example, the O- would be more polar than the O-H (assuming the molecule is the same). Its nice to imagine the electro-static potenial maps some chemistry books have to decide whether one is more/less polar. So the O- will have much more negative charge than the O-H and will make the molecule overall more polar.

(I dont know for sure, but I think a case where the deprotonated version would be less polar might be benzene with an alcohol substituent which has the negative charge resonance donated.)

With your other example, NR4+, the individual bonds may have some polarity associated with them, but the overall molecule would be classified as non-polar since the Dipoles cancel out int he tetrahedral structure (assuming the R groups are the same; if not, there will be an overall dipole).

To make a statement as to whether hydrogen bonding or charge is more important in determing solubility in a substance is difficult. I would say that generally though, if it is a question of an alcohol vs the deprotenated version, the ion will be more soluble. Comparing dis-similar substances would require you to take the whole structures into account though.

Hopefully I got at what you were asking and this helps.
 
Yes, that helped, thanks. I meant different Rs for my NR4 example, but I guess the nonpolarity of the R groups would supersede the polarity of a positive charge. Would O- make stronger H bonds than N-? same with ROH vs. RNH2?
 
Honestly, I have no idea. I know in that other thread they were talking about something similar, and I looked at the wikipedia page which states that Nitrogen has stronger Hydrogen bonds than Oxygen, but that is only in the gas phase, and typically solvents drastically affect free energy change. Sorry, thats not really a helpful answer at all, but I'll try and see if there is a more solid answer.
 
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