An introduction to the structure and uses of alcohols
So far you will probably have met two homologous series of organic compounds:
Alkanes- saturated hydrocarbons- general formula CnH2n+2
Alkenes- unsaturated hydrocarbons- general formula CnH2n
Well you are about to meet another homologous series- The alcohols.
In naming the alkanes and alkenes
you have met so far you may have noticed that the first part of their
names were similar. Well there is a reason for this; the first part of the name will help you in
identifying the number of carbon atoms found in an organic compound. So for example; the prefix meth- will tell
you the compound contains 1 atom of carbon, while the prefix oct- will tell you the molecule has 8
atoms of carbon. Just as the names of all the alkanes
end in the three letters -ane and the names of all alkenes end in -ene, the names of all the alcohols end in -ol. The prefixes
you will have used to name alkanes and alkenes are shown in the table below. These prefixes also indicate the number of carbon atoms present in a molecule.
Prefix
meth
eth
prop
but
pent
hex
hept
oct
non
dec
number of carbon atoms
1
2
3
4
5
6
7
8
9
10
The table above gives the prefixes used for naming organic compounds with up to nine carbon atoms.
Just as all alkenes molecules contain the functional group C=C and
all alkanes contain the functional group C-C,
well all alcohols contain the hydroxyl functional group C-O-H or C-OH; you may see it written both ways. It is
the presence of this hydroxyl group (C-OH) which gives the alcohols
their characteristic properties.
The most widely used alcohol is ethanol; this is the
alcohol which is used in alcoholic drinks. Ethanol is made in a process called fermentation. Fermentation is a natural process; it is a form of
anaerobic respiration where the sugar glucose is turned into the alcohol ethanol and carbon dioxide gas, equations for fermentation are shown below:
glucose(aq) → ethanol(aq) + carbon dioxide(g)
C6H12O6(g) → 2C2H5OH(aq) + 2CO2(g)
The table above can help you name the first ten alcohols.
The first alkane was methane to name the first alcohol remove the -e from
the end of the alkane methane and replace it with -ol and you have the first alcohol; methanol. Similarly the second alkane was ethane,
the second alcohol is ethanol, also propane becomes propanol, butane becomes butanol etc.
Ball and stick models of the first four alcohols,
methanol, ethanol, propanol and butanol are shown below along with their structural formulae.
The first four alcohols
The alcohols form a homologous series with the
general formula CnH2n+1OH. The displayed formula and the structural formula for the
first 5 alcohols are shown below. You should note all
alcohols contain the hydroxyl functional group (C-OH) and it is this group which determines how alcohols
react with other substances.
Uses of alcohols
The main uses of alcohols are in alcoholic drinks (ethanol only) such as wine, beer and spirits and as a solvent in cosmetics, perfumes and paints. Alcohols are flammable and they make excellent fuels. In the UK the petrol sold at the pumps is a
mixture of petrol and up to 10% ethanol, some racing cars even run on a 85:15 % mixture of petrol to ethanol.
Perhaps one of the most high profile for uses for alcohol at the moment is as a hand sanitizer in gels and wipes to kill corona-virus.
Key Points
Alcohols form a homologous series of compounds with the general formula CnH2n+1OH. Alcohols all contain the hydroxyl functional group.
Alcohols are named from the corresponding alkane by replacing the -e from the end of the alkane name with -ol.
Other common uses of alcohols include: as solvents in many cosmetics and perfumes. However perhaps the most common use of alcohols is that of ethanol
in alcoholic drink and hand sanitizers.
