Right. Okay. Now, we’re going to be talking
about alcohols. They have the general formula
of ROH, when R is an alkyl group and OH is
a hydroxyl group in this context.
In a moment, we’ll be talking about the
The origins of alcohol stems from the name
al-kuhl in Arabic meaning volatile.
The nomenclature is shown here. In the example
of 3-methyl-1-butanol, the final ‘e’ of
the alkene homologous series is replaced with
the -ol suffix “ol”. In this scenario,
as we said before, when we actually have a
group which takes priority, the numbering
system relates to the carbon to which it’s
nearest. In this case, the OH is attached
in the case of the 3-methyl-1-butanol in the
terminal position. The carbon to which the
OH is attached, therefore, takes the number
1 counting backwards along the longest chain
2, 3, 4. This gives you 3-methyl-1-butanol.
When we have cyclic alcohols, such as in the
case of cyclopentanol, we put cyclo in front
of the name and the suffix remains the same.
At the bottom, you can see some examples of
what are known as methyl alcohols: primary,
secondary and tertiary.
The methyl-1 has only one member of its family
which is methanol. We’ve come across this
The second one, where the OH group is attached
to the terminal carbon on an alkane chain,
is the primary alcohol. In this case, butan-1-ol
although sometimes you’ll see it referred
to as n-butanol.
The secondary alcohol, where indeed the OH
is attached to a carbon which bears two alkyl
groups, would, in this case, be butan-2-ol,
otherwise known as sec-butanol.
And finally, the tertiary to which the OH
is attached to a carbon-bearing 3 alkyl groups
on it. In this case, the old nomenclature
would have been tertiary butanol. However,
the correct IUPAC nomenclature is 2-methylpropan-2-ol.
The structure of an alcohol can be shown here.
And as we discussed in the previous lecture
about haloalkanes, you can see that we have
got an alpha carbon, to which the OH is directly
attached, and also a beta carbon.
Pay particular attention to the polarisation
of the oxygen-hydrogen bond shown in this
case. This, of course, is a sigma molecular
orbital and you have electronegativity on
the oxygen which pulls electron density with
it so that the oxygen itself is delta negative
or partially negatively charged and the hydrogen
is delta positive or partially positively
This is important in the physical and chemical
characteristics of this class of compound.