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    I've been searching online everywhere to find the answer to my Q but I can't find anything so basically, I'm looking over the nucleophilic substitution mechanism with ammonia being the nucleophile. I understand so far that the ammonia attacks the carbon atom, causing the carbon-bromine bond to break, leaving a carbocation with the ammonia in place of the bromine atom and a positive charge on the nitrogen. But I don't understand the next step, where another ammonia molecule comes along and attacks the hydrogen atom instead of the positive nitrogen?!?!?!?! Why does it attack the hydrogen??? (( Please help !!!!!
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    The process where another other ammonia takes a proton to neutralise the alkylmmonium ion to a neutral alkylamine is reversible and exists in a equilibrium.

    If you think about how the +ve charge on the N will effect the electron density around it, and the polarity of the H bonds, the reasoning for attacking an H should become clear.
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    (Original post by alow)
    The process where another other ammonia takes a proton to neutralise the alkylmmonium ion to a neutral alkylamine is reversible and exists in a equilibrium.

    If you think about how the +ve charge on the N will effect the electron density around it, and the polarity of the H bonds, the reasoning for attacking an H should become clear.
    so the positive charge on the N means that it will be trying to attract electrons? So electron density is greater around the N than the H, meaning there is a small positive charge on the H? Is that wrong?
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    (Original post by slothgenius)
    so the positive charge on the N means that it will be trying to attract electrons? So electron density is greater around the N than the H, meaning there is a small positive charge on the H? Is that wrong?
    That's how I'd rationalise it. You should probably also think that the N already has 8 electrons around it so will be quite a poor electrophile. With reactions where a nucleophile attacks a Nitrogen, one of the other bonds to the nitrogen pretty much always breaks (e.g. in an oxaziridine the N-O bond breaks) to allow the new group to attach. In your reaction, you would have to release a carbanion or hydride which is really unfavourable.
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    (Original post by alow)
    That's how I'd rationalise it. You should probably also think that the N already has 8 electrons around it so will be quite a poor electrophile. With reactions where a nucleophile attacks a Nitrogen, one of the other bonds to the nitrogen pretty much always breaks (e.g. in an oxaziridine the N-O bond breaks) to allow the new group to attach. In your reaction, you would have to release a carbanion or hydride which is really unfavourable.
    Thank you so much for the help!
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    (Original post by slothgenius)
    Thank you so much for the help!
    No problem
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    (Original post by slothgenius)
    I've been searching online everywhere to find the answer to my Q but I can't find anything so basically, I'm looking over the nucleophilic substitution mechanism with ammonia being the nucleophile. I understand so far that the ammonia attacks the carbon atom, causing the carbon-bromine bond to break, leaving a carbocation with the ammonia in place of the bromine atom and a positive charge on the nitrogen. But I don't understand the next step, where another ammonia molecule comes along and attacks the hydrogen atom instead of the positive nitrogen?!?!?!?! Why does it attack the hydrogen??? (( Please help !!!!!
    hey- you PM'd me about uni advice but I can't reply because I think you've disabled private messages, just wondering where you'd like me to reply?
 
 
 
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