Right. Physical and chemical properties.
Let’s have a quick look here at the electronegativity
of nitrogen and relate it to its reactivity.
As we’ve seen before, where we have a species
which is more electronegative than carbon,
it polarises the carbon heteroatom bond.
In this case, on the Pauling scale, the electronegativity
of carbon is 2,550 and the electronegativity
of nitrogen is 3,066. What this results in
is a dipole moment, as you can see here, where
the bond is polarised. And a partial negative
charge resides on the nitrogen and a partial
positive charge resides on the carbon on the
alkyl or aryl group.
Amines form intermolecular hydrogen bonds,
not unlike alcohols and also carboxylic acids.
They can also form hydrogen bonds with water
and as a result, amines with a linear chain
shorter than three carbons are soluble in
water. Again, the common odours that you will
find which directly result from amines are
fishlike odours, for example, things like
C5 and C6 containing amines, methylamine and
ethylamine, which smell similar to ammonia,
in general. But, it is also important to aware
there are a lot of long-chain mono and diamine
compounds, compounds such as putrescine and
cadaverine. And obviously, they correlate
to the smells of decomposing bodies.
Stereochemistry of nitrogen.
If you recall, when we looked at carbon, we
had four electrons which could be hybridised
or found in hybrid orbitals. Here, in case
of the nitrogen stereochemistry, we could
also have sp3 hybridisation. However, unlike
in the case of the carbon, we have a lone
pair which occupies one of those… which
occupies a… one of those hybridised orbitals.
As a consequence, what we see here is a pyramidal
structure, which is common to both ammonia
and all of the amines that you see. The nitrogen
is at the apex of the pyramid and the other
groups are at each apex of a triangular base.
The end is sp3 hybridised, like a sp3 hybridised
carbon. But, one of the sp3 positions is occupied
by the lone pair, which is shown at the top
of that pyramid structure here.
What’s also worthy of note is that theoretically,
if we have different substituents attached
to each of those posts, we would then have
a nitrogen to which is attached four different
things: a lone pair and then three substituents.
And the mistake that can be made sometimes
is thinking that, therefore, it’s possible
to achieve chirality or optical isomerism,
as we observe in the case of a carbon with
four different substituents on it.
The reality in the case of amines and ammonia
is that you actually get a flipping of that
molecule. And so, you never actually see one
particular enantiomeric form of a nitrogen
appearing. It should be also be stressed that
the bond angles between the substituents are