Chemical Ideas 13.2 deals with alcohols and ethers.
Key terms in this chapter are:
Alcohol.
Ether.
Alcohol group (hydroxyl group).
Polyhydric alcohol.
Skeletal structure.
Phenol (and phenols).
Hydrogen bond.
Miscible.
Polar solvent molecule.
Non-polar hydrocarbon chain.
Alkoxy group (-OR).
Volatile.
Flammable.
In this section you are going to learn:
•
That alcohols and ethers are structural isomers.
•
That alcohols as a homologous series of organic compounds.
•
How to name alcohols and polyhydric alcohols.
•
How to draw skeletal structures for alcohols.
•
How to recognise a phenol and distinguish between alcohols and phenols.
•
Why alcohols, like ethanol and methanol, are very soluble in water.
•
Why alcohols become less soluble in water as the homologous series is ascended (the non-polar hydrocarbon chain gets longer).
•
Why ethers are more volatile than alcohols and why ethers are not very soluble in water.
An alcohol and an ether can share the same molecular formula, but their structures
(structural formulae) are different. That is they are structural isomers. For example, the molecular formula C
2
H
6
O represents both ethanol (an alcohol) and methoxymethane (an ether).
Examine the above two structures. They each have a different functional group . It is the functional group that determines the homologous series to which an organic compound belongs.
For alcohols the functional group is the -OH group (called the alcohol group or hydroxyl group). The general formula of an alcohol is C n
H
2n+1
-OH, where n (the number of carbon atoms) is 1, 2, 3, 4, etc. Ethanol, C
2
H
5
OH or CH
3
CH
2
OH, is the most common alcohol (where n = 2).

For ethers the functional group is an oxygen atom bonded to two carbon atoms,
C-O-C. The general formula of an ether is C n
H
2n+1
-O- C n
H
2n+1
, where n = 1, 2, 3, 4, etc. The simplest ether, that is, the first member of the ether homologous series is methoxymethane (where n = 1 for both alkyl groups).
Q1.
Draw the structure of ethoxyethane. Draw a structure for each of the alcohols that are structural isomers of this ether (there are 4).
You can think of alcohols as being derived from alkanes by substituting an -H atom for an -OH group. Here are some more examples of alcohols and how they are named.
Q2.
Name each of the alcohols in the answer to Q1.

Polyhydric alcohols have more than one -OH group. For example:
Sometimes skeletal formulae are used for organic compounds. For example, the dihydric alcohol below is pentane-2,3-diol.
Q3.
Draw the skeletal structure of each of the alcohols in the answer to
Q1.
The following is not an alcohol. It is a phenol because the -OH group is attached directly to a benzene ring.
You can also think of an alcohol as forming from water by swapping a -H atom of a water molecule for an R- (alkyl) group.
The polar O-H bond of the alcohol molecule makes it polar like water molecules.
Furthermore, the strongest kind of intermolecular bonding, called hydrogen bonding , exists between alcohol molecules. This results in an alcohol having a higher boiling point than an alkane of similar relative molecular mass. For example, ethanol (M r
=
46) is a liquid and propane (M r
= 44) is a gas.

Hydrogen bonding between alcohol molecules and water molecules also explains the high solubility of alcohols in water. Methanol and ethanol are miscible is water in all proportions, but as the non-polar hydrocarbon chain gets longer the alcohol becomes considerably less soluble in water.
You can think of an ether as being derived from an alkane by replacing a -H atom by an alkoxy group (-OR).
You can also think of an ether as forming from water by replacing both -H atoms of a water molecule with alkyl groups. Another ether molecule is shown below:
Ether molecules are polar but hydrogen bonding is not possible between them. A weaker kind of intermolecular bonding exists between their molecules making them volatile and flammable. Nor can ether and water molecules hydrogen bond, and so ethers are only slightly soluble in water. Ethers do mix well with non-polar solvents such as alkanes.