In the previous lecture, we talked about the
reactions of amines with carboxylic acid derivatives
so that we could form amides, a very important
functional group, both in terms of chemistry
and also in biology. But, it’s important
that we actually deal with amines on their
own to some extent, not least because they
form some… they form some of the most
important chemicals within our body.
Okay. So, let’s first and foremost look
at the nomenclature. First and foremost, where
we have an amine, which consists of an alkyl
or aryl group, represented here as “R”, we
use the longest chain, as we do in all cases.
So, in other words, if it was two carbon units,
it would be ether; three would be propyl;
four would be butyl; and so on and so forth.
And then we remove the “e” at the end, and
we attach the suffix “-amine”. There is sometimes
a number prefix to indicate the position of
the amine on the chain by the lowest possible
number. What does that actually mean? Well,
let’s have a look at a couple of examples.
If we look at 2-pentylamine, you can see what
I said before. When you have a substituent
on a long chain, as you’ve seen here, where
you’ve got a pentane chain, five carbons
in length, what we need to do is find the
carbon to which the hetero atom is attached.
In the case of alcohols, it is OH. In the
case of haloalkanes, it is chlorine, bromine
or fluorine. And in the case of amines, it
is nitrogen. Nitrogen has an atomic mass of
14, carbon of 12, therefore, nitrogen takes
priority. When, of course, the nitrogen is
in a terminal position, then of course, it
is that carbon to which it’s attached that
takes the number 1.
However, when we’re looking at a nitrogen
which is substituted in the middle or close
to the end of a long chain, we need to consider
the terminal and call that “1”. So what that
affectively means is that the amine, the NH2
group in 2-pentylamine, is in the second position,
hence the name “2-pentylamine.”
It’s also worthy of note that when you’ve
actually got substitution on the nitrogens
themselves, note we have here NH2, those Hs
can be replaced by other alkyl or aryl groups,
as in the case of N,N-dimethylethylamine.
Note the location of each of the components.
The bottom right hand corner, you see that
abbreviated formula: CH2CH3. This is the origin
of your ethylamine. The fact that we have
a substitution on the nitrogen by two methyl
groups means that it is N,N-dimethyl, where
we have on a single nitrogen, two dimethyl
Sometimes you’ll actually see where we have
more than one nitrogen: an N and an N’, indicating
the awareness that we have that there are
two nitrogens in our system.
In terms of nomenclature, it’s also important
to realise that there are different types
of substitution and they refer to primary,
secondary or tertiary depending on the number
of carbons attached. The simplest possible
arrangement is ammonia where we have a nitrogen
to which we have covalent bonds, sigma bonds,
to three hydrogen atoms, shown here. And that
is the simplest possible nitrogen base.
The next one up is where we have substitution
of one of those hydrogens with either an alkyl
or an aryl group, thus leaving NH2. This is
a primary amine. Further substitution by another
alkyl or aryl group, shown in this case as
R’, would be a secondary amine.
And then finally, substituting all three hydrogens
results in a tertiary amine where, in this
case, the final hydrogen has been replaced
with what we’ve designated here as R’’.
Bear in mind that just because we’ve given
these different denotations in terms of R,
R’ and R’’, they could all be the same alkyl
or aryl group; it’s just for the sake of