Chemistry only

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 C_nH_2n+2
Alkenes- unsaturated hydrocarbons- general formula C_nH_2n

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

alcoholic drinks are made by fermenting the sugars present in grapes.

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. 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

3d models to show first the structure of methanol, ethanol, propanol and butanol.

The alcohols form a homologous series with the general formula C_nH_2n+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.

Structural formula, molecular formula and displayed formula for the alcohols methanol, ethanol, propanol, butanol and pentanol.

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 C_nH_2n+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.
One of the main uses of alcohols is as fuels. Alcohols are very flammable and release large amounts of energy when combusted.
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.

An introduction to the structure and uses of alcohols

The first four alcohols

Uses of alcohols

Key Points

Practice questions

Check your understanding - Questions on alcohols

Next