Amine in Sn2 part 2 Amine continuing to act as nucleophile to generate more products
Amine in Sn2 part 2
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- In the last video, we saw that amines are actually reasonably
- decent nucleophiles.
- And, in particular, we saw some ethylamine attack some
- bromoethane in an Sn2 reaction.
- And right after that happened, we had some diethylammonium
- because the nitrogen had given away an electron to this
- carbon right over here.
- So it had a positive charge.
- And so you had diethylammonium bromide.
- The bromine had left, taking an electron.
- It then had a negative charge.
- And then we said that that could actually be in
- equilibrium, where another ethylamine goes and takes a
- hydrogen from the diethylammonium and turns that
- into diethylamine.
- So we essentially had a primary amine turn into, or I
- guess you could say, converted into a secondary amine.
- Now, the one thing that might have popped into your brain
- near the end of that video is, hey, isn't this also a good
- And you say look, it's got this lone pair.
- It's more electronegative than the things
- that it's bonded with.
- Maybe this too could do a nucleophile attack or maybe
- some type of an Sn2 reaction.
- And you would be correct.
- So you could imagine, if you have some more bromoethane
- hanging around-- let me draw some more bromoethane.
- So let me draw it like this.
- So this is our bromo group.
- And then let's say we have a hydrogen above like that.
- That's kind of upside down from the last one we
- did, but same idea.
- Then we have another hydrogen behind, just like that.
- And this is obviously a carbon.
- You could imagine that now you have this diethylamine.
- It can have an Sn2 reaction with the bromoethane.
- So before it was just the ethylamine.
- Now it's the diethylamine that's acting as a
- So this electron right here in yellow could be given to this
- carbon right at the same time that this bromine leaves and
- takes that electron.
- And the bromine already had one, two, three, four, five,
- six, seven valence electrons.
- And this is really almost identical to what happened in
- the previous video, except now we are starting with a
- secondary amine, and we're going to see it's going to
- turn into a tertiary amine, as opposed to the last one, where
- we started with a primary amine and turned into a
- secondary amine.
- So what's this going to look like after
- we've done the attack?
- So the bromine will have left.
- It's now the bromide anion.
- So now we have the bromide anion.
- It has its seven original valence electrons and now it
- took one more electron from the carbon.
- It now has a negative charge.
- And now this ethane group right here-- so this carbon
- right here is this carbon right over here-- is now going
- to be attached-- let me draw it this way.
- It's now going to be attached to this nitrogen.
- So this yellow electron is now attached to that carbon, and
- it's bonded to that green electron, which on the
- nitrogen or that the nitrogen has.
- And then this nitrogen has two other ethyl groups attached to
- it, one, two, and then it also has this hydrogen over here.
- And because this nitrogen gave away an electron, it now has a
- positive charge.
- And I didn't draw these two hydrogens here on this carbon;
- they're implicit.
- I could draw them.
- One hydrogen, one hydrogen, and then another hydrogen.
- But just to keep things simple, I'm going to leave it
- off, just so it becomes very clear
- that we now have triethyl.
- Let me make this clear.
- So we have one, two three ethyl groups.
- So now this is triethyl and it's a
- positively charged nitrogen.
- It's bonded to four things.
- And essentially, it has given away an electron, so this is
- And if you view it as being an ionic compound with the
- bromide, then you would call this triethylammonium bromide,
- which this would be the salt version, the ionic compound
- right there.
- But we have our triethylammonium, and then you
- could imagine, we had that ethylamine
- floating around before.
- If you still have enough of that ethylamine floating
- around-- so let me draw some of that ethylamine.
- Ethylamine looks like this.
- It has two hydrogens.
- It has a lone pair.
- It has a slightly partially negative charge right here.
- Nitrogen is very electronegative.
- It's the most basic of the neutral functional groups that
- we've studied.
- It might want to capture this hydrogen proton, so it
- captures it by giving it its electron.
- And then that electron that was associated with that
- hydrogen atom is now given back to this nitrogen.
- And now, once again, I'll draw this as being in equilibrium.
- I'll do this in equilibrium because one could swipe the
- hydrogen from the other.
- But now this guy over here becomes ethylammonium.
- So I'll draw-- so this is what he was before.
- And now he's bonded to this hydrogen.
- So now he's bonded to this green hydrogen over here.
- Let me make this green just here.
- So that's ethylammonium.
- And we saw this in the last video: ethylammonium.
- And then this guy right over here, and, of course, you have
- the bromide floating around, but this guy over here now is
- just a nitrogen bonded to three ethyl
- groups: one, two, three.
- It lost its hydrogen, gained an electron, so it's now
- neutral again.
- And so this guy is triethylamine.
- And since he gained that electron, he had an electron
- here, an electron there, so this is the electron that he
- already had and that magenta electron he gets back, and he
- has a lone pair.
- So you might say, hey Sal, but couldn't this guy, couldn't
- triethylamine act as a nucleophile?
- And you would be right.
- So the triethylamine, if you still have some of that
- bromoethane hanging around-- so let me draw some
- And obviously, there's some hydrogen here.
- There is some hydrogen here.
- If you have some more of that bromoethane hanging around,
- this guy could then attack that bromoethane and then you
- would be left with-- what would that look like?
- Let me do it in that same color.
- So in that green color, you have the nitrogen.
- It has its three original ethane groups or ethyl groups
- that's attached to it.
- It has this electron.
- But it's now bonded to this carbon over here.
- And let me be very clear.
- This was an Sn2 reaction.
- So right when it attacks that carbon, this bromine, and we
- saw this multiple times, can take that other electron from
- the carbon, and so this becomes another bromide anion.
- I'm going a little bit faster than I've done in the past
- because we've seen this many, many, many, many times.
- And now this guy is attached to this ethyl group.
- So this ethyl group I could just draw like this.
- He gave this carbon, this magenta electron there, and so
- we have this new bond.
- And I could also draw the hydrogens.
- We have this hydrogen and this hydrogen.
- We could draw them off like this, hydrogen and hydrogen,
- but that makes the drawing a little bit more confusing.
- But what just happened?
- This guy gave away an electron.
- Let me make it clear.
- He gave away an electron so he has now a positive charge.
- You have the bromine turned into bromide.
- It took an electron.
- But what is this now?
- This is tetraethylammonium.
- So we have four.
- It's a quaternary ammonium.
- So this is tetra, tetra for four: one, two, three, four.
- Ammonium, instead of amine, because it has
- that positive charge.
- The nitrogen has four bonds.
- It's given away an electron.
- Tetraethylammonium, and then if you view it as a salt with
- the bromide anion, it's tetraethylammonium bromide.
- So the whole point of this video and the last video is--
- in the last video, I just wanted to show you that an
- amine, it's reasonably basic.
- It can act as a nucleophile, and show you how it would
- react, show you the mechanism.
- But what I wanted to show you in this video is that that
- reaction just keeps going.
- And so when you start with the original ingredients, when you
- started with the ethylamine and the bromoethane, you might
- say, oh, this is pretty simple.
- You're just going to end up with a little bit of
- But the reality is you're going to end up with all of
- this stuff.
- It's going to be all mixed up in every different way.
- You're going to end up with some diethylamine in there.
- You're going to have some ethylamine in there.
- You're going to have some ammonium in there.
- You'll have some triethylammonium in there.
- You'll have some ethylammonium.
- in there.
- You're going to have a little bit of everything.
- Oh, let me be clear here.
- I just want to make sure I didn't
- misname any of this stuff.
- Yes, I think I named it right.
- Sometimes I get confused with the ammoniums and amines.
- But the whole point of this is that this reaction can keep
- going and this Sn2 reaction can keep occurring in a bunch
- of different ways.
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