All right guys, so we just talked about how you can use aqueous acid to add alcohols to
double bonds through acid catalyzed hydration.
But it turns out that there's actually more than one way to add alcohols to double bonds
and that's actually a huge focus of this section.
So what I'm going to do now is I'm going to show you guys an alternate reaction that we
could use that also adds alcohols to double bonds and it's called oxymercuration demercuration.
So first of all, what you're going to notice is that this is just a really long name for
a reaction, so I personally like to shorten it and I always call it instead of that long
name, I usually just call it oxymerc and that's fine.
If you just say oxymerc, that just means it's oxymercuration demercuration or reduction,
it's fine.
In general, what do we see?
What's the general reagents that we use for this?
What we're going to find is that you have a double bond of course.
And then we're going to react it with this weird reagent that's a mercury with two acetate
or acetyl groups on it.
So that's what OAc means, it means acetyl group, so I'll show you what that looks like
in a second.
So you have that and you have water.
So this is really the first step and this is called the oxymercuration step.
Now if you're confused how you'd remember this, well, eventually you are going to need
to memorize this.
But one way the I like to maybe make it simpler is that notice that the word oxymercuration
has mercury in it.
Mercury.
And notice that the reagent of oxymercuration is Hg, which is mercury.
So whenever you just see the Hg, you automatically know this is an oxymercuration.
In fact, we won't see any other reactions with mercury until orgo two, so you're pretty
safe that if it's a mercury, that's oxymerc.
Then the second step of this is to react with NaBH4 and some kind of base like NaOH.
This is called the reduction step or the demercuration step.
Now, typically, that's the way things work when you have something above the arrow and
something below it.
That could even mean that you have a reagent and its solvent or that you just have a two-step
reaction.
Sometimes you're going to see these written as separate steps like one and two.
But sometimes you'll just see it written without the numbers and you're just supposed to know
that what's on top of the arrow is the oxymerc part, what's at the bottom is the reduction
part.
Regardless, we're going to learn these reagents.
Don't worry.
But regardless, look what happens.
We still get an alcohol.
So let's go ahead and look at the general feature of this mechanism.
So basically the intermediate for oxymerc is not going to be the same as hydration.
Instead of being a carbocation what it's going to be is what we call a bridged ion.
And that's going to be a big deal when it comes to predicting products.
That's actually going to matter a lot.
The stereochemistry here is actually going to matter.
It's going to be decisively anti.
So what that means is that anti-stereochemistry is the same way of saying that at the end,
you're going to get trans products.
So if you ever hear me say anti, that just means that at the end, you're going to expect
your alcohol and your H to be trans to each other.
Like I just told you guys, the products are alcohols.
So now let's come to the last two facts.
Would we expect there to be rearrangements in this mechanism?
Remember that rearrangements happen when you have carbocations.
Do we have a carbocation?
No.
So it turns out that this reaction is actually not going to have any rearrangements because
it doesn't have any carbocations.
I'm just going to write that right here.
No carbocations.
So there's actually no way for it to rearrange at all.
Finally, is it going to follow Markovnikov's regiochemistry?
Yes, it is.
Markovnikov's rule is still going to apply even though it's not a carbocation.
It's still going to apply.
So now when we look down at out general products, it actually makes sense what it looks like.
Notice that what I have – oops, just a second.
Notice that what I have is that once again this is my Markovnikov location and I attach
my alcohol to it.
So my alcohol is going to go Markovnikov.
On top of that, notice that the H that I added on the other side is going towards the dash
and the OH is going on the wedge.
What that means is that I have a Markovnikov anti-alcohol.
Does that make sense?
Because basically, it's Markovnikov because it went to the most stable location.
It's anti because my H and the OH that I added are trans to each other and it's an alcohol.
So even if you didn't know the full mechanism you can still predict the products just based
on these facts.
But obviously, we need to know the mechanisms.
Let's go ahead and get started with that.