Right. Okay. So, now, I would like to talk
to you about a very key functional group and
that is the carbonyl functional group. Here,
we can see on the board two examples of carbonyl
functional groups, the aldehyde and the ketone.
Note the difference between the two.
In the case of the ketone, we have a single
substitution on the carbonyl carbon. This
is the carbon double bond oxygen with the
remaining valency on that carbon being taken
up by a carbon-hydrogen sigma bond. In the
case of the ketone, however, we have substitution
on both sides, either via a mixture or combination
of aromatic and aliphatic substituents.
Going back to what we said about aromatics,
of course, benzene rings, naphthalene etc.
or indeed alkyl rings such as methyl, propyl
or butyl and this fundamentally informs how
they react and also some of their properties.
So, let’s have a look at carboxyl compounds
just briefly. There will be a lecture, the
next lecture, that covers other reactivity
of these carboxyl compounds, but I want to
introduce right now the concept of them because
they feature our friend, the carbonyl functional
group, where we have R as an aliphatic or
aromatic joined to a carbon double bound to
an oxygen, and it is this that actually informs
the reactivity both of carbonyl and carboxyl
reagents due to the properties of the carbon
double bound to the oxygen.
I’ve shown here Z correlating to a group
or groups which can be attached to that carbon
such as the OH group, the OR or alkoxy group,
the NR or amine group that’s giving us an
amide and a hydride which can be formed from
another equivalent of acetic or alkanoic acids
and indeed, halide group. I’m not going
to go into too much detail in this lecture,
suffice to say that their reactivity is based
to a large extent on the properties of that
So, let’s have a look at some of the nomenclature.
The ending, for example, of a ketone, the
suffix is always “–one”. A ketone group
is numbered to give the carbonyl group the
lowest number. Remember what we said before
about priority. We were talking, in this particular
case, about what the atomic mass was or the
heteroatom attached to a carbon.
So, let’s, for example, look at our friends,
the aldehydes, shown at the top. Propanal
is... and butanal take the “–al” suffix
because they are aldehydes. So, whenever you
see a carbonyl group in a terminal position
to which is attached only hydrogen, you should
be able to recognise it as being an aldehyde.
Now, because the carbon-oxygen bond there
shows that the oxygen actually has a mass
of 16, the carbon has a mass of 12, this gives
the priority to the carbon of 1 and of course,
therefore, every subsequent backward count
would move around from that position all the
way to the longest chain.
So, in the case of the carbonyl, we would count
1, 2, 3 all the way around to where the methyl
group is in the 3 position. If we have a look
at the ketone, we can see that in the case
of propanone or acetone, there is no need
to number it, since you cannot have a ketone
in a terminal position because it then becomes
an aldehyde. So, there is no need to say propane-2-one
because there is only one possible position
for that carbonyl to be in and still remain
If, on the other hand, we have these long
chain asymmetric ketones such as the 3-methyl-2-hexanone,
we use the same rules that we’ve applied
in the nomenclature of haloalkanes and of
alcohols earlier on in this module. That is
to say where we have an oxygen, a heteroatom
attached to the carbon, where it is not the
terminal position, we find the nearest terminal
position to call one. We do use that in the
case of OH when it is not terminal and we
do that in the case of halogens when they
are not terminal.
So, this, therefore, gives us a counting structure
which goes from the terminal, there is the
carbonyl 1, 2, 3 all the way through the hexane
longest chain and the substituent in the 3
position, which is the methyl group, carries
that prefix 3-methyl-2-hexanone where the
2 correlates to exactly where the carbonyl
fits in the longest chain of that alkane structure.