Alcohols are a functional group consisting of an −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 R−OH, where R is any alkyl or substituted alkyl group.
Ethanol (C2H5OH) is a small, two-carbon alcohol. Ethanol is the "alcohol" in beer, wine, and liquor. Ethanol is the most common alcohol solvent used in chemistry labs.
A phenol is a benzene ring where a C−H bond is substituted for a hydroxyl group, giving a 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.
Phenol (C6H5OH) is an organic molecule in which the hydroxyl group is attached to a benzene 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 −OH is attached to only one other carbon. In a secondary alcohol, the carbon attached to the −OH is attached to two other carbons. In a tertiary alcohol, the carbon attached to the −OH is attached to three other carbons.
A primary alcohol is attached to a carbon that is attached to just one other carbon atom. 1-propanol (CH3CH2CH2OH) is a primary alcohol. A secondary alcohol is attached to a carbon that is attached to two other carbons. Propan-2-ol (CH3CHOCH3) is a secondary alcohol. A tertiary alcohol is attached to a carbon that is attached to three other carbons. 2-methylpropan-2-ol (CH3)3COH) is a tertiary alcohol.
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 −OH group. The name will depend on the number of carbon atoms. Then replace the terminal -ane with -anol.
2. The position of the −OH group is indicated by a number in the prefix, using the lowest number possible.
In 2-hexanol (C6H13OH), the hydroxyl group (−OH) is attached to the second carbon. However, 5-hexanol is not an acceptable name. Choose the locant (location of substituent) that gives the lowest carbon number possible.
In 3-hexanol (C6H13OH), the hydroxyl group (−OH) is attached to the third carbon. However, 4-hexanol is not an acceptable name. The correct name is based on the locant (location of substituent) that gives the lowest carbon 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 −OH group creates an alcohol.
3. Numbers indicate the position of groups attached to the parent chain.
In 2-methyl-1-butanol (C5H11OH), the methyl group is attached to the second carbon, and the hydroxyl group is attached to the first carbon.
2-bromo-3-methyl-1-hexanol (C7H14BrOH) has a bromine attached to the second carbon, a methyl group attached to the third carbon, and the hydroxyl group attached to the first carbon.
