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- I told you, in the last video, that
- epoxides are very reactive.
- That this little triangle right here, this equilateral
- triangle, is highly strained, highly unstable.
- So it makes it want to do something, get out of this
- configuration.
- What I want to do, in this video, is
- to show you a reaction.
- What we have, right here, and we saw this in the last video.
- I've drawn a couple of more hydrogens.
- And I've actually drawn a little bit of the three
- dimensional nature of the bonds right here.
- Because it'll matter.
- This is cyclo-.
- And remember, you can just pretend like this triangle
- here, if it was replaced with a double bond, this would be
- cyclohexene.
- But because, instead of a double bond right here, we
- have these bonds to this oxygen, this
- is cyclohexene oxide.
- Let's think about what would happen if we had some
- cyclohexene oxide mixed in with water.
- And we have some type of maybe acid catalyst in there.
- So it will allow some extra hydrogen
- protons to float around.
- So we have water.
- But since we actually put some acid catalyst there-- and it
- could really be any acid catalyst, anything that would
- increase the hydrogen proton concentration-- we're more
- likely to have some hydronium ions floating around.
- And we know what hydronium ions look like.
- They look like water with an extra proton, with an extra
- hydrogen on them.
- So hydronium ions look like this.
- This is water.
- Let me do it in a different color since I already used the
- blue for the cyclohexene oxide.
- So this is water right here.
- What happens to get hydronium is the oxygen in the water
- takes a proton from someplace else, from some acid, the acid
- catalyst, in this case.
- It would essentially give an electron to it.
- If this electron gets given to some hydrogen proton, the
- ending result will look like this.
- You have a bond formed with another hydrogen.
- And now, you have a positive charge.
- You have a positive charge on the oxygen because it gave
- away an electron.
- This is hydronium.
- We've seen it many times.
- And this is what results if you put an acid in water.
- It will increase the hydronium concentration.
- You'll see more and more of this.
- So what's likely to happen if we have cyclohexene oxide with
- water as a solvent, but we also have a good amount of
- hydronium floating around?
- The more acid we put in, the more hydronium we'll have.
- Well, a possible reaction is, well let's see, this oxygen is
- just as likely, or it may want to get a hydrogen proton just
- as much as a hydronium.
- So if they bump into each other in the exact right way,
- this oxygen, right here, could give an electron to that
- hydrogen right there.
- And then the original, this orange hydronium, or this
- orange oxygen right here, can take its electron back.
- If that happens, what do we end up with?
- Well, let's see.
- So if that happened, now we have-- Let me draw this
- original molecule.
- It will no longer be cyclohexene oxide exactly.
- Because it just got a hydrogen proton.
- It's an intermediary now.
- Let me try my best to draw it though.
- All right.
- We have that.
- Then, we have the oxygen popping out of the page.
- It had these two extra electron pairs, but now it
- gave one of its electrons to this proton.
- So now, it gave one of its electrons to this hydrogen
- right here.
- I call it a proton, because a hydrogen without an electron
- is just a proton.
- It doesn't have another neutron inside of the nucleus.
- So you have the hydrogen over there.
- Now, since this oxygen gave away an electron, it now has a
- positive charge.
- Let me draw these two purple hydrogens that
- are behind the page.
- So that's one hydrogen there.
- One hydrogen there.
- Obviously, there's other hydrogens on these carbons.
- But if I drew it, it would take a while.
- It would make a whole diagram messy.
- But it's always assumed that a neutral carbon
- will have four bonds.
- And of course, this thing right here is now just water.
- This thing took its electron back.
- I'll draw it here.
- This thing took its electron back.
- And now, it's water.
- It could be this one.
- But there's obviously tons of water around.
- So I could even draw other water molecules.
- It doesn't have to just be that one.
- Now, what is a likely to happen?
- And this is the fun part of this reaction.
- Because it's actually something we've seen before.
- It's a reaction that we've seen many, many times already.
- But it's just not obvious when you see it in this form.
- When you look at this molecule, right here, what's
- going on here?
- Well, I already told you that I have this highly, highly
- strained bond here.
- It's like this equilateral triangle.
- The bond angles are closer than they want to be.
- The electrons want to get away from each other.
- If you try to do this with a chemistry model, it would
- actually strain the plastic or the wood of the chemistry
- model to actually make it.
- On top of that, this oxygen with this extra hydrogen now,
- it is actually a good leaving group.
- And so now, it's probably triggering some things in your
- brain about the type of reaction that might occur.
- And think about this carbon right here.
- Think about this carbon.
- Actually, these two carbons are the same.
- So I'll just pick on this one, the bottom one, for fun.
- Think about this carbon right here.
- It is bonded.
- It's a secondary carbon.
- So it would not be super great for an Sn2 reaction.
- But you can have an Sn2 reaction with a secondary
- carbon, especially when the leaving group wants to leave
- bad enough.
- So if one of these water molecules, it didn't have to
- be this first one right here, if it just bumps into this
- carbon in the exact way, it can actually act as a
- nucleophile.
- Water isn't, traditionally, a very strong nucleophile.
- But it can be a nucleophile, especially if the leaving
- group is ready to leave and this is a
- really strained bond.
- So what you could imagine is that this
- water gives an electron.
- It loves this carbon nucleus right there.
- It gives it to that carbon.
- And since that carbon is getting an electron from this
- water over here, then it can release an electron back to
- this oxygen, making it neutral.
- So it can release this back to this oxygen right here.
- What will we end up with then?
- Now, something interesting has just happened.
- And this is typical of all Sn2 reactions.
- Remember, it's Sn2.
- We're substituting with a nucleophile.
- Water is a weak nucleophile.
- But, in this case, it'll stick better than this thing that's
- all strained.
- And we call it 2, Sn2, because both of the reactants are
- involved in the rate determining step.
- This is the rate determining step right here.
- So what do we end up with?
- Let me just draw the hexane ring, just like that.
- Now, all of a sudden, this oxygen up here, what
- will it look like?
- Well, this bond gets broken.
- It takes back an electron.
- So you only have this bond to the oxygen, this top bond to
- the oxygen.
- That's the oxygen right there.
- It took this electron back.
- So now, it has this electron and the electron that was
- bonded to the carbon.
- So it has a pair of electrons.
- And then, it's bonded to that hydrogen that it took from the
- hydronium in the first step.
- And then it's bonded to this hydrogen over there.
- So it really is just an OH group now, bonded right that.
- It's popping out of the page.
- You still have this hydrogen that's going behind the page.
- But since we had a Sn2 reaction, you can imagine this
- came from the back.
- And this let go from the front.
- So what will now happen is, this hydrogen that was kind of
- behind the page, now will pop forward.
- Because this guy went from even behind that hydrogen.
- So this hydrogen, over here, will now pop forward.
- So this hydrogen, now, has popped forward.
- I'll circle it just so you see it's the same hydrogen.
- But it has popped forward, since this guy, this
- nucleophile attack, happened from the back.
- And now, he is attached.
- He has attached down here.
- This water has attached.
- Well, it's not water anymore.
- So you had the oxygen.
- Two hydrogens.
- And then it had two pairs.
- But now, one of the pair turns into a bond.
- Because it gives this electron there.
- So these two guys are bonded.
- This electron is given to the carbon.
- And the bond is behind the page now.
- Just like that.
- And then the final step is-- now, since this guy gave an
- electron, he has a positive charge here.
- Just to make it nice and clean, you can imagine another
- water molecule comes and takes one of those hydrogens away
- from this guy.
- All these hydrogens are just getting passed around between
- these water molecules.
- So you can imagine this water molecule
- could take that hydrogen.
- This oxygen takes the electron back, and
- then becomes neutral.
- And then our final product-- we are now done--
- will look like this.
- So we had cyclohexene oxide, a reactive epoxide, in water
- with some acid around.
- So it kind of catalyzed the leaving group and all that.
- We just saw that in this.
- But what does the resulting molecule look like?
- So popping out of the page up here, we have an OH.
- That's this right here.
- I'm just simplifying a little bit.
- Going behind the page, we have a hydrogen right over there.
- And then, popping out of the page we have a hydrogen.
- So popping out of the page, right
- here, we have a hydrogen.
- And then, behind the page, we have another OH group.
- So we've made a diol.
- And, in particular, if we wanted to name this thing
- right here, we have our cyclohexane ring.
- That's our main ring.
- We have cyclohexane.
- And then, we have OH groups on the-- We
- can just start numbering.
- We want to start numbering where the groups are.
- So we call this the 1, 2, 3, 4, 5, 6 carbon.
- We have OH groups at the 1 and the 2 carbons.
- So we have two of them.
- So it's a diol.
- So we call this, 1 comma 2-diol, because
- we have two OH groups.
- Diol.
- The -ol is for alcohol when you have these OH groups.
- We have two of them.
- And they are on opposite sides.
- This alcohol, or this OH, is popping out of the page.
- This OH is behind the page.
- So if we really wanted to be specific about even the
- stereochemistry here, we would call this trans.
- They're on opposite sides.
- One is in front.
- One is behind.
- So this is trans.
- This is trans-cyclohexane-1,2-diol.
- So, hopefully, you enjoyed that.
- What the fun thing about this is, one, to see that epoxides
- are reactive.
- You just even see a new reaction.
- But the really fun thing to see is that these Sn2
- reactions keep popping up.
- In fact, the ones we learned, Sn2, Sn1, E1, E2, these just
- keep, over and over, popping up in chemistry in places
- that, maybe it wasn't obvious at the first glance.
- But then, when you actually think about it, it's actually
- perfect for that type of reaction.