For this section, I’m going to be introducing
a completely new type of organic reaction,
and that’s the condensation reaction.
Whenever you get two molecules that are spontaneously
combining to form a bigger molecule with the
loss of a smaller molecule on the side, that’s
what’s called a condensation reaction.
There’s actually tons of different types of
condensation reactions in organic chemistry.
But the specific ones that we’ll be dealing
with in this section have to do with enolates.
Remember that enolates are the negative anions
of a deprotonated alpha-carbon.
What we find is that enolates are going to
be a part of the condensation because enolates
are so reactive that they’re not only just
going to react with electrophiles as we’ve
talked about in the past.
They’re also even going to be able to react
with each other or with themselves to do something
that’s called self-condensation.
Obviously, due to the fact that this is an
enolate-mediated reaction, alpha-protons are
required for this type of reaction to take
If you don’t have an alpha-proton, then you’re
not getting an enolate because an enolate
is the deprotonated version of an alpha-carbon.
I want to just back it up for a second and
go back to what we know and use that information
to inform our understanding of condensation
Back in the day, it seems like the glory days
now, we learned about nucleophilic addition.
We learned that carbonyls were especially
reactive at the carbonyl carbon, nucleophiles
We would get a mechanism called nucleophilic
addition where a tetrahedral intermediate
We would get an alcohol as a result.
We did that a lot.
More recently, what we’ve learned is that
certain types of nucleophiles specifically
basic ones are going to react at the alpha-carbon
and take away a proton.
We’ve noticed that for example OH negative
can remove an alpha-proton and make what we
call an enolate anion, a negative charge on
that alpha carbon.
What’s special about that negatively charged
enolate is that now we know that it can attack
It could attack some alkyl halide, or some
We can get an alpha-substituted carbonyl.
What we’re going to learn in this section
is how enolates relate to condensation reactions.
It turns out that same thing when a base deprotonates
an alpha-carbon, you’re going to get an
But what happens when you don’t have an electrophile
to react with?
What happens in the absence of an electrophile?
What if I just make my enolate but then there’s
nothing to react it with?
I never add that other alkyl halide or that
What do we do?
In that case, that special case, where there
is no electrophile, then the enolate is going
to react with itself.
What we’re going to find is that the enolate
is going to react with the non-enolated version
It’s going to do a nucleophilic addition
making a tetrahedral intermediate on the other
Isn’t that interesting?
Basically, this acts as the nucleophile for
another nucleophilic addition.
What we wind up getting is a condensation
reaction because now I’m taking two ketones
or aldehydes and combine them together into
one larger molecule.
Notice what I would get here, just for this
tetrahedral immediate, what I would get is
now R here, r here.
I would get a negative charge.
That negative charge would eventually deprotonate
This is the product of enolate condensation.
This is what we’re going to be focusing on
for quite a few videos.
We’re going to be spending a lot of time
on enolate condensation.
I want to give you some examples.
This is going to kind of be a preview of what
we’re going to be learning in a little bit.
It turns out that ketones and aldehydes can
combine together to make molecules that have
alcohol components and a carbonyl.
This reaction in particular is called an aldol
The reason being that as we’ll see more
later, there’s part alcohol and there’s
It’s an aldol reaction.
Notice this is condensation because I’ve
got two smaller molecules combining to form
a bigger one.
What if we do this with two esters.
We take two esters.
We make an enolate, they react with each other.
They’re going to make a beta-dicarbonyl specifically
a beta-keto ester.
This reaction is called a Claisen condensation.
This is a preview.
You’re not supposed to learn these here.
I’m just trying to show you guys how we’re
going to be dealing with a lot of reactions
that condensate with enolates.
These are two of the most important but we’re
going to deal with a lot more in this section.
That being said, I hope the general mechanism
makes sense so far.
Let’s move on to our first condensation reaction.