nucleophilic substitution with ammonia

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pondering-soul
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So I saw the mechanism for nucleophilic substitution with ammonia. What I don't understand is when ammonia forms a covelant bond with the carbon atom (the lone pair is attracted to the carbon atom and a covelant bond is formed) why does the nitrogen atom not get a + charge but the H atom does instead?

As you can see for the hydration of ethene, when the oxygen atom joins onto the carbon cation (the lone pair forms a covelant bond with the carbon atom) the oxygen gains a positive charge. My guess is that this is because the previous lone pair is now being used in the covelant bond so it's electron density is being 'shared'. But if that's the case, why doesn't the nitrogen atom in the ammonia mechanism become positively charged? Why instead does the hydrogen get the positive charge?
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EierVonSatan
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(Original post by pondering-soul)
So I saw the mechanism for nucleophilic substitution with ammonia. What I don't understand is when ammonia forms a covelant bond with the carbon atom (the lone pair is attracted to the carbon atom and a covelant bond is formed) why does the nitrogen atom not get a + charge but the H atom does instead?
That image is hilariously wrong, is that from a text book? :laugh: Nitrogen should have the positive charge.
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pondering-soul
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(Original post by EierVonSatan)
That image is hilariously wrong, is that from a text book? :laugh: Nitrogen should have the positive charge.
damn... wtf....
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Plantagenet Crown
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(Original post by pondering-soul)
So I saw the mechanism for nucleophilic substitution with ammonia. What I don't understand is when ammonia forms a covelant bond with the carbon atom (the lone pair is attracted to the carbon atom and a covelant bond is formed) why does the nitrogen atom not get a + charge but the H atom does instead?

As you can see for the hydration of ethene, when the oxygen atom joins onto the carbon cation (the lone pair forms a covelant bond with the carbon atom) the oxygen gains a positive charge. My guess is that this is because the previous lone pair is now being used in the covelant bond so it's electron density is being 'shared'. But if that's the case, why doesn't the nitrogen atom in the ammonia mechanism become positively charged? Why instead does the hydrogen get the positive charge?
Yeah....that’s really bad. I suspect it was a typo though as there’s no way people writing this (who must be trained chemists) would make such nonsensical errors unless they were sleep deprived or drunk or something. It should absolutely be the nitrogen with a positive charge, nitrogen is always positive when bonded to 4 other atoms. And hydrogen is always neutral when covalently bonded to another atom.
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Pigster
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(Original post by Plantagenet Crown)
And hydrogen is always neutral when covalently bonded to another atom.
My memory is fuzzy and I've been drinking, but isn't one of the resonance structures of diborane involve H+?

Or am I just trying to be awkward?
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charco
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(Original post by Pigster)
My memory is fuzzy and I've been drinking, but isn't one of the resonance structures of diborane involve H+?

Or am I just trying to be awkward?
The boranes aren't chemistry...
They are witchcraft.
Banana bonds?
Multi-centre bonds?
Nidos?
My University had a research professor specialising in novel boron compounds, so we had a full unit dedicated to witchcraft and magic potions.The only thing I learned is that decaborane is five times more borane than diborane.
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Plantagenet Crown
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(Original post by Pigster)
My memory is fuzzy and I've been drinking, but isn't one of the resonance structures of diborane involve H+?

Or am I just trying to be awkward?
Not sure, but as charco says, boranes are so damn weird and I remember I hated learning about multi-centre bonds in inorganic chemistry as there never seemed to be much logic to it, it was just a case of "memorise this". I'm an organic chemist where chemistry is actually chemistry
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