Alcohols
What is here?
Alcohols are organic compounds that:
- contain the hydroxyl functional group, —OH
- have molecules based on alkanes in which one of the H atoms is replaced by an —OH group
- form a homologous series which has the general formula CnH2n+1OH.
Use your mouse (or finger on touch devices) to move or scale molecules. Double tap to stop and start each animation.
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methanol, CH3OH
ethanol, C2H5OH
propan-1-ol, C3H7OH
propan-2-ol, C3H7OH
Homologous series
A homologous series is a series of compounds which:
- have the same functional group
- have the same general formula
- differ by CH2 in molecular formulae from neighbouring compounds
- show a gradual variation in physical properties, such as their boiling points
- have similar chemical properties.
Functional groups
A functional group is an atom, group of atoms or a bond responsible for the characteristic chemical reactions of a substance. The functional group in alcohols is most easily shown as —OH.
General formulae
A general formula is a chemical formula used to represent the members of a homologous series. The general formula for the alcohols is CnH2n+1OH
Hexanol molecules, for example, contain six carbon atoms:
n = 6
2n + 1 = (2 × 6) + 1 = 13
So the molecular formula for hexane is C6H13OH.
Structural and displayed formulae
A structural formula shows the number of atoms of each element in a molecule, and their positions in the molecule.
A displayed formula shows the same information as a structural formula, but in addition it shows the bonds between the atoms.
| Name of alcohol | Structural formula | Displayed formula |
|---|---|---|
| methanol | CH3OH |  |
| ethanol | CH3CH2OH |  |
| propan-1-ol | CH3CH2CH2OH |  |
| propan-2-ol | CH3CH(OH)CH3 |  |
Isomers of butanol
Isomers are substances that have the same molecular formula, but a different arrangement of atoms:
- propan-1-ol and propan-2-ol are position isomers in which the hydroxyl group is found in different positions on the carbon chain.
The molecular formula of butanol is C4H9OH. Butanol has four isomers:
- butan-1-ol and butan-2-ol
- 2-methylpropan-1-ol and 2-methylpropan-2-ol.
The molecular models here show these four isomers. Two of them have branched carbon chains.
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