Alcohols can be represented by the general formula `ROH`, where `R` is any alkyl or substituted alkyl group. The group may be primary, secondary, or tertiary; it may be open chain or cyclic; it may contain a double bond, a halogen atom, or an aromatic ring. For example, as shown in Fig.

All alcohol contains the hydroxyl (`-OH`) group, which, as the functional group, determines the properties characteristic of this family. Variations in structure of the `R` group may affect the rate at which the alcohol undergoes certain reactions, and even, in a few cases,may affect the kind of reaction.

When the hydroxyl group is attached directly to an aromatic ring they are phenols, and differ so markedly from the alcohols that we shall consider them separately.

Alcohols are classified as mono, di and trihydric alcohols depending upon the number of `- OH` groups present in them. Alcohols with one, two and three `-OH` groups are called mono, di and trihydric alcohols respectively. Alcohols, which contain four or more hydroxyl groups attached to the `sp^3` hybridised carbon atoms are called polyhydric alcohols.

The monohydric alcohols can further be classified according to the type of carbon that bears the `- OH` group. An alcohol in which `-OH` group is attached to carbon atom, which in turn is linked to only one carbon atom, is called primary `(1^o)` alcohol. Similarly, an alcohol in which `-OH` group is attached a carbon atom which is linked to two carbon atoms is called secondary `(2^o)` alcohol and an alcohol in which the carbon atom bearing `-OH` group is attached to three carbon atoms is called tertiary `(3^o)` alcohol. For example, see Fig 3 ,

For the simpler alcohols the common names, are most often used. These consist simply of the name of the alkyl group followed by the word alcohol. For example, see Fig.(iv).

We should notice that similar names do not always mean the same classification; for example, isopropyl alcohol is a secondary alcohol, whereas isobutyl alcohol is a primary alcohol.

`A)` Select as the parent structure the longest continuous carbon chain that contains the `-OH` group; then consider the compound to have been derived from this structure by replacement of hydrogen by various groups.

The parent structure is known as ethanol, propanol, butanol, etc., depending upon the number of carbon atoms; each name is derived by replacing the terminal `-e` of the corresponding alkane name by `-ol`

`B)` Indicate by a number the position of the `-OH` group in the parent chain, generally using the lowest possible number for this purpose.

`C)` Indicate by numbers the positions of other groups attached to the parent chain as show in Fig C 1.

Alcohols containing two hydroxyl groups are called glycols. They have both common names and IUPAC names as shown in Fig C 2. Common names are given in parenthesis as shown in Fig C 3.