Why is nitrogen basic while oxygen and flourine are not?

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Main Question or Discussion Point

Nitrogen is a lewis base because it has a lone pair of electrons with which to form bonds with electrophiles. Oxygen has 2 lone pairs of electrons and halogens have 3. Why doesn't oxygen use any of its spare pairs of electrons to react with electrophiles?
 

Answers and Replies

  • #2
Ygggdrasil
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Oxygen and fluorine are more electronegative than nitrogen, so it is less favorable for these atoms to share their lone pairs with an electrophile. This is not to say that it is impossible, for example, alcohols get protonated at very low pH (around -1 to -2).
 
  • #3
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I want to say that Flourine is waaaaaaaaaay too reactive / unstable. . . it never exists as an ion irl.
 
  • #4
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Ygggdrasil: that explains it, thanks.

Highway: So the F- ion is uncommon is it? I've read that HF is a weak acid but I don't know what its dissociation constant. Are you saying that HF doesn't actually dissociate at all?
 
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turbo
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Ygggdrasil: that explains it, thanks.

Highway: So the F- ion is uncommon is it? I've read that HF is a weak acid but I don't know what its dissociation constant. Are you saying that HF doesn't actually dissociate at all?
HF is a very strongly reactive acid that can break down lots of oxides and can etch glass.
 
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Ygggdrasil
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HF has a pKa of 3.17. Compared to the other halides (e.g. HCl pKa ~ -7, HBr pKa ~ -9), this is quite a high value. So, HF will dissociate, but not to the same extent as related compounds.
 
  • #7
DrDu
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Nitrogen is a lewis base because it has a lone pair of electrons with which to form bonds with electrophiles. Oxygen has 2 lone pairs of electrons and halogens have 3. Why doesn't oxygen use any of its spare pairs of electrons to react with electrophiles?
Who sais so? H+ is quite electrophilic and readily reacts with H2O to form hydronium ions H3O+ and also FH2- forms stable salts. Other electrophiles? I think there are adducts of BF3 and various ethers. And of course you can make all kinds of electrophilic substitutions on oxygen. So its more a question of stability of the adducts with respect to further reactions. Finally there are salts like trimethyloxonium tetrafluoroborate (Meerwein salt).

Btw. its fluorine, not flourine.
 
  • #8
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Ygggdrasil: that explains it, thanks.

Highway: So the F- ion is uncommon is it? I've read that HF is a weak acid but I don't know what its dissociation constant. Are you saying that HF doesn't actually dissociate at all?
I remember this coming up in class and our prof saying that F- exists for only a very short time in solution, due to it's high reactivity.

Email your prof the same question -- he'll give you a better answer than I can, as I'm not a chemist.
 

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