orgo question

[ssh18]

I have a question about nucleophilic addition reactions. When an aldehyde or a ketone reacts with a primary amine in an acidic solution, it produces an imine. What if the primary amine structure is such that there are two primary amines on both sides and a carbonyl group in the middle. Which N would act as the nucleophile? The one that's closer to the carbonyl or farther away? and what's the reason behind it? Thanks!!

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[ssh18]

anyone? please!

 

[adamber]

I have a question about nucleophilic addition reactions. When an aldehyde or a ketone reacts with a primary amine in an acidic solution, it produces an imine. What if the primary amine structure is such that there are two primary amines on both sides and a carbonyl group in the middle. Which N would act as the nucleophile? The one that's closer to the carbonyl or farther away? and what's the reason behind it? Thanks!!

Are you asking if the carbonyl has two primary amines attached to it, and it attacks the carbonyl on itself? If that's the case, it would no longer be a primary amine, it would be secondary. But if you are asking about that molecule attacking a different regular carbonyl, it would probably be equal amounts for either amine to be the nucleophile, since the R group of it is the carbonyl for both of them.

 

[iA-MD2013]

so...im not sure exactly what the nucleophile is from your description...but let me give you a general rule...
a better nucleophile (for forming the imine) is one that has very avaible lone pairs. for that reason, amides would be the worst (draw a resonance structure). whatever your starting material is, the most electronegative atom would be the nucleophile. in determining that, you need to look at both the inductive effect and resonance.

 

[ssh18]

Sorry, I wasn't very clear on the question.
Here's what I meant to say:

If any aldehyde or ketone reacts with a primary amine (NH2NHCOCNH2) where the carbon is double bonded to the oxygen, which N attacks the electrophilic carbon of either the aldehyde or the ketone since there are two N's in this primary amine that can potentially attack it..and why?

Thanks!

 

[iA-MD2013]

ahh i see....
the nitrogen on the very left would be the nucleophile. the reason is that the other 2 are amides, and those are very unreactive (their lone pairs are unavailable. draw resonance forms to see this).

 

[ssh18]

Thanks soo much! I drew it out and it's making sense now. I also drew out the resonance structures for amide and I think I understand this but I just want to make sure. So when the electrons are delocalized (like in a resonance structure), they are typically less reactive just like in the amide where the electrons on the N delocalize with the carbonyl double bond?
Also, the 2 pair of lone electrons on the oxygen, do they take any part in delocalization?

 

[iA-MD2013]

Thanks soo much! I drew it out and it's making sense now. I also drew out the resonance structures for amide and I think I understand this but I just want to make sure. So when the electrons are delocalized (like in a resonance structure), they are typically less reactive just like in the amide where the electrons on the N delocalize with the carbonyl double bond?
Also, the 2 pair of lone electrons on the oxygen, do they take any part in delocalization?

exactly! if the electrons are delocalized, then they aren't as available to react...and it makes it a crappy nucleophile. this is because the definition of a nucleophile is that it has a lot of electrons (which is why negatively charged nucleophiles are typically better)
the electron pairs of the oxygen on any carbonyl will never take part of the delocalization because you can never use those electrons in a resonance form. try it.
hope that helps

 

[ssh18]

nice!! I tried it out and now I get it...those electrons don't move around so they can't take part in resonance. Thank you so much for helping. You are wonderful!

 

[iA-MD2013]

no problem! i'm glad i was able to help