Which compound has the greater electron density on its nitroge...

Question

Which compound has the greater electron density on its nitrogen atom?

Two chemical structures with nitrogen atoms, questioning which has greater electron density on nitrogen.

Accepted Answer

Hello everyone. Let's do this problem and says which of the following compounds has the greatest tendency for nitrogen to donate an electron pair. So we have four different compounds that are all rings that have nitrogen z either in the ring or attached to the ring. So let's think about what gives the compound, the greatest tendency to donate an electron pair or I should say what makes an Adam have the greatest tendency to donate an electron pair. So having the greatest tendency to donate an electron pair means having the most available electrons, right? And do you think the most available electrons are going to be shared with other atoms? No. Right. I forgot to mention this also means that they'll have the highest electron density, right? So more electrons to be shared, highest electron density and more available electrons, which means they're not being shared. So this tendency and electron density can be increased or decreased by residents. So that sharing can either work in the favor of that atom in terms of being able to donate electrons or against it. So other atoms can either donate their electrons towards the atom in question, or if it is sort of stealing those electrons from that atom due to resonance and that will decrease the electron density and make them less likely to donate an electron pair. So we want to look at if these compounds have resonance and see how that affects the electron density of the nitrogen atom. Let me move all this text down a little bit. Mhm So starting with a, we have a lone pair on nitrogen, right? Because we see nitrogen has 123 single bonds. So 246 valence electrons, it needs eight and that would be 12345 electrons touching it which makes nitrogen happy is their resonance in this compound. No, there are no pi electrons that can be that can make this compound conjugated. So that means the nitrogen has one lone pair able to donate, there's no resonance to affect that. So we have to sort of compare it to the other compounds to be able to tell anything else. So compound b nitrogen will have a lone pair again. But this time in the five member ring, we have a double bond on that carbon neighboring the nitrogen. So we have a little bit of resonance. This lone pair can swing down to create a carbon nitrogen double bond. This lone pair will swing onto that neighboring onto the next carbon giving us the following structure. That carbon now has a negative charge with an extra loan pair. And this nitrogen only has four bonds for electrons touching it. So that nitrogen now has a positive charge. So you see in this case, the resonance is decreasing nitrogen electron density. So do you think that's going to make this nitrogen more likely to donate an electron pair? No, right. So that can we can eliminate B as an answer choice. So, so far A is the most likely because it has no resonance looking at compound, see that nitrogen has a lone pair. And this time we have two pi bonds. So that's even more resonance, right? Again, the electrons, the lone pair on nitrogen are swinging down into the ring. And I'm not going to draw all the resonance structures out, but these pi bonds can move. And there are a lot of resonant structures possible here since it's a five member ring. So all of those resonant structures are going to create a more positive nitrogen. Let me just draw the first resonance structure to show you what I mean there. Oops. So we would have a negative charge on the carbon in the ring, positive charge on the nitrogen. Now, so you see, again, the nitrogen is becoming more positive losing electron density and then these electrons can swing down and we have more resonance structures that can be formed, but we won't draw all those. So again, all in all that's going to decrease the electron density of the nitrogen. So eliminating answer choice C and lastly answer choice D nitrogen has a lone pair and we have a fennel group attached to the nitrogen. So that screams resonance to me, right, those electrons are going to want to jump into that ring. And we can have several resonance structures with these pi bonds being de localized all throughout that ring. Actually, let me do the same thing I did with C I'll show one resonant structure to demonstrate nitrogen becoming more positive. So we have NH two plus double bonded to the Benzene Ring. Now, lone pair on that carbon In this one pair can have all these transformations that I drew before. So again, that nitrogen is losing electron density due to the resonance. So we can eliminate answer choice D which leaves answer choice A to be the correct answer for this problem and has the most available electron pair that can be donated. That's it for this one. I hope this video is helpful and thanks for watching.

Which compound has the greater electron density on its nitrogen atom?

Key Concepts

Electron Density

Electronegativity

Resonance Structures

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