# Structure and IUPAC Nomenclature

Alcohols are a functional group consisting of an ${-}{\rm{OH}}$ attached to an sp3-hybridized carbon. In IUPAC nomenclature, alcohols are indicated by changing the suffix from -ane to -anol. A number indicates the location of the alcohol. Alcohols have priority for numbering over all other groups except for carbonyls (ketones, aldehydes, carboxylic acids, etc.).
An alcohol, also called a hydroxyl, is a hydrocarbon containing a hydroxyl functional group. The hydroxyl group is attached to an sp3-hybridized carbon. Functional groups are groups of atoms responsible for the characteristics of a molecule. Generally, the formula is ${\rm {R{-}OH}}$, where R is any alkyl or substituted alkyl group.
A phenol is a benzene ring where a ${\rm {C{-}H}}$ bond is substituted for a hydroxyl group, giving a ${\rm {C{-}OH}}$ unit. Another way to think of it is as an alcohol in which the hydroxyl group is attached to a benzene ring. Phenols belong to the class of aryl alcohols in which a hydroxyl group is attached to an aromatic ring.
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on the type of carbon to which the hydroxyl group is attached. The classification of alcohols directly affects the characteristics and reactions of alcohols. In a primary alcohol, the carbon attached to the ${-}{\rm{OH}}$ is attached to only one other carbon. In a secondary alcohol, the carbon attached to the ${-}{\rm{OH}}$ is attached to two other carbons. In a tertiary alcohol, the carbon attached to the ${-}{\rm{OH}}$ is attached to three other carbons.
In simpler alcohols, common names are generally used. The common name consists of the alkyl group followed by the word alcohol. For example, CH3CH2OH is referred to as ethyl alcohol, and CH3CH2CH2OH is referred to as propyl alcohol.

However, the International Union of Pure and Applied Chemistry (IUPAC) establishes the standards for nomenclature. IUPAC applies the following rules for naming alcohols.

1. Select the parent chain that contains the ${-}{\rm{OH}}$ group. The name will depend on the number of carbon atoms. Then replace the terminal -ane with -anol.

2. The position of the ${-}{\rm{OH}}$ group is indicated by a number in the prefix, using the lowest number possible.

### Examples of Some Simple Alcohols

Compound Name Molecular Formula Corresponding Alcohol Name Molecular Formula of the Alcohol
Methane CH4 Methanol CH3OH
Ethane CH3CH3 Ethanol CH3CH2OH
Propane CH3CH2CH3 Propanol CH3CH2CH2OH
Propane CH3CH2OH 2-propanol CH3CHOHCH3

Replacement of a hydrogen on an alkane with an ${-}{\rm{OH}}$ group creates an alcohol.

3. Numbers indicate the position of groups attached to the parent chain.