Ketone naming - Aldehydes and Ketones, Organic Chemistry Video Lecture - Class 11 | Best Video for Class 11

In the last video, we learned a
little bit about aldehydes.
And we saw that they have the
general structure where you
have a carbonyl group bonded to
some type of carbon chain,
or I guess in the simplest form,
this could just be a
hydrogen over here, and then
they definitely will have at
least one hydrogen bonded to
the carbon in the carbonyl
group, so this was
an aldehyde.
Now, very closely related to
an aldehyde is a type of
molecule called a ketone.
And let's draw a couple of
ketones just to make things
clear, and then we'll think
about what the difference is
between a ketone and
an aldehyde.
So this right here, CH3, CH3,
carbon right over here.
This right here is a ketone.
And you say, hey, Sal,
that looks very
similar to an aldehyde.
I have a carbonyl
group in both.
So this right here is
a carbonyl group.
This right here is
a carbonyl group.
Let me write this: carbonyl.
We have a carbonyl
group in both.
We have a carbon chain
over here.
This could be a general
carbon chain here.
We have a methyl group.
So how is this different?
And I think you'll see.
It's this part that I haven't
highlighted yet.
In an aldehyde, there's
two ways to
think about an aldehyde.
You could either say that, look,
the carbonyl group is at
the end of a carbon chain.
So the next thing over is
going to be a hydrogen.
Or you could say that in an
aldehyde, you have at least
one hydrogen bonded to
the carbonyl carbon.
And the way I remember that, so
you have a hydrogen there,
and in the ketone you don't.
The carbonyl group is embedded
in a carbon chain.
It is bonded to-- at least it
is bonded to a carbon on
either side, so over here
you have a carbon.
And the way that I remember the
difference, and this is
really just a little bit of a
mnemonic just to memorize it,
is aldehyde has an "h" in it.
There's an "h" right over there,
and an aldehyde has a
hydrogen bonded to
this carbon.
So now that we at least have a
reasonable understanding of
what a ketone is, let's
name a few, just
to familiarize ourselves.
So this right here is the
simplest possible ketone.
And it's called acetone, or
that's its common name.
And actually, the word ketone
comes from the German word for
acetone, which was I think
instead of a "c" there, they
had a "k," so it's
like aketone.
And they said, oh,
this is a ketone.
So this is the common name.
Another kind of traditional or
common way of naming a ketone
is to name each of these groups,
and it's kind of
similar to the way that
we named ethers.
But instead of writing the
word ether at the end, we
write the word ketone.
So here we have a methyl group,
and we have another
methyl group, so we have two
methyl groups right over here.
So this would be dimethyl
ketone.
This right here is
dimethyl ketone.
And then if you wanted the
systematic way of naming it,
you just look at the longest
carbon chain, which is one,
two, three carbons,
so it's prop.
Propa-, and instead of calling
it propane, we get rid of that
"e" over there and we would
call it propanone.
That tells us that this right
here is a ketone.
And you have to know where
this double bond is.
And actually, for propanone, you
don't have to specify it,
because if you know it's a
ketone, you know that it has
to have a carbon on either side
of the carbonyl group, so
you actually don't even have
to specify where the
carbonyl group is.
But if you wanted to, you could
say, OK, that's going to
be on the two carbon.
No matter what direction you
start counting from, it's
going to be on the two carbon.
But the two is kind of optional
for propanone.
Let's do a couple
of other ones.
So let's say we had a molecule
that looks like this.
So the traditional way of naming
it, you'd say, OK, on
this end of the ketone, I have
one, two, three carbons.
So on that end, I have
three carbons.
That is a propyl group.
And on this other side of the
ketone right over here, I have
only one carbon.
That is a methyl group.
So then you would
just name them.
And you name then in order
of increasing chain size,
molecule size, or group size.
So this one you'd write methyl
first. Methyl, because it's
only one carbon.
So this is methyl
propyl ketone.
This is kind of the traditional
or the common way,
often kind of the most used way,
of naming this molecule.
But the systematic way of naming
it, you look at the
longest carbon chain and you
say, OK, I have one, two,
three, four, five carbons.
So it's going to be pent-.
And then you want to start
numbering it so that the
carbonyl carbon has the lowest
possible number.
So you want to start numbering
on the right side: one, two,
three, four and five.
So this right here, so we said
the prefix would be pent-.
So it's penton, and instead of
saying it's pentane, you say
it's pentanone.
And to specify where the
carbonyl group is,
you say it's 2.
This is 2-pentanone.
And you might also see
it written like this:
pentan-2-one.
Either one of these right here
would be acceptable.
Let's do a slightly more
complicated example.
Let's say we had something
that looked like this.
So we have something,
a molecule,
that looks like this.
And let me stick some
chlorines over here.
So what would this be?
Well, our longest chain, once
again, is this cyclohexane:
one, two, three, four,
five, six carbons.
And I'll just name this
systematically right here.
And the more complicated
things get, the more
systematic people will
want to name it.
So if we have six carbons right
here, and they're in a
chain, so this is cyclohexane.
You'd put the "e" there
if this carbonyl
group wasn't there.
But since it is, we would call
this cyclohexanone, So this
right here tells us to name
it cyclohexanone.
And then in a ring like this,
this would implicitly be the
number one carbon.
So if this is the number one
carbon and we want to number
in the direction so that the
next groups have the lowest
possible number, so we want to
make this the two carbon.
So this is
2,2-dichlorocyclohexanone.
Now, there's two more.
And I'll just show these to you
because these tend to be
referred to by their
common names.
So I just want to show them to
you real fast. One is this
molecule right here, where
we have a methyl group
on this side: CH3.
And over here, we have
a benzene ring.
Now, that first super simple
ketone that we saw, we called
this acetone.
And so the common name here is
actually derived from acetone.
Instead of calling it acetone,
because it doesn't have just a
methyl group here, this is
called aceto-, and instead of
acetone, it's acetophenone,
because we have this phenyl
group, that benzene
ring right there.
Acetophenone, which is a pretty
common molecule, and
you'll see it referred
to this way.
Now, the other one that you
might see every now and then,
and I just want to expose it
to you, is a molecule that
looks like this, that has
two benzene rings on it.
It looks like that.
And this is benzophenone.
These last two I just really
wanted to expose you to their
common names.
But, in general, I think you
have a decent idea at this
point of how to name at least
the simpler chains, either
with the common names, for
example, propyl, or methyl
propyl ketone, or 2-pentanone.
And these are the more
typical or maybe the
easier naming examples.