Now that we understand the general mechanism
of nucleophilic addition, it’s important
to really understand those specific nucleophiles
that can attack carbonyls and make substituted
One of the most famous of these is cyanide.
Cyanide is a negatively charged nucleophile
that’s used to make a functional group called
You may already kind of be able to guess what
that is just by the name but I’ll show you.
Typically, CN is reacted as a negatively charged
NaCN is very common but you could also see
This is a very common way to represent it
As you can imagine, this is just straight
up nucleophilic addition.
I’ve got my CN negative, I’ve got my very
strong partial positive charge so I get a
nucleophilic addition mechanism.
What this is going to make is a negatively
charge oxide and my CN substituent.
That is what I get after the first step.
Then there’s always going to be a protonation
step that you can use.
You can use water or some kind of mild acid
Obviously that’s not the mechanism for protonation.
We’ll do something like this and like that
and you would get your functional group.
Your functional group, whenever you have a
CN and an OH on the same geminal to each other,
that’s called a cyanohydrin.
I wanted to inform you that there’s another
form of CN that’s actually pretty common
as well that doesn’t require a protonation
I just wanna show you guys another example
would be if I use HCN.
HCN is a really interesting compound because
if you just look at it, you might think “Oh,
that’s a source of CN negative.”
But remember that the carbon-hydrogen bond
is actually a very strong bond.
Usually carbon and hydrogen doesn’t just ionize
that’s actually a covalent bond.
Covalent bonds usually don’t just disassociate
to make H plus and CN negative.
That’s kind of strange.
Why would it do such a thing?
The answer has to do with acidity.
It turns out that it’s not that it’s a weak
bond in terms of polarity, that there’s a
But it turns out that this is a very acidic
It turns out that HCN, if you guys remember
your pKas way back in the day, it has a pKa
of about 10.
In normal aqueous environments, it’s going
to be ionized.
It’s going to be in an ionized form.
The advantage of using HCN is that look what
You’ve got the CN negative and you’ve
also got your proton to protonate.
You could do NaCN and then water or you could
just use HCN and HCN will take care of both
It will do the nucleophilic addition and you’ll
go ahead and you’ll add your hydrogen for
the protonation step.
Now what I want to do is I specifically want
to talk about two other reactions that happen
with cyanohydrins that really have nothing
to do with the nucleophilic addition.
But as a functional group, we should be aware
of what can you do to a cyanohydrin.
That’s what we’re going to do in the next
Let’s go ahead and start off with the first