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.
The models show members of this series with 1 – 4 carbon atoms. You can also see the structural and displayed formulae for these alcohols.

Use your mouse (or finger on touch devices) to move or scale molecules. Double tap to stop and start each animation.

Options
atom labels
ball and stick model
space-filling model
perspective view

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 alcoholStructural formulaDisplayed formula
methanolCH3OH
ethanolCH3CH2OH
propan-1-olCH3CH2CH2OH
propan-2-olCH3CH(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.

Options
atom labels
ball and stick model
space-filling model
perspective view

butan-1-ol

2-methylpropan-1-ol

butan-2-ol

2-methylpropan-2-ol

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Alcohols

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