Primary, secondary and tertiary are the three main types of aliphatic chain alcohols in organic chemistry. Phenols are aromatic compounds featuring an –OH group attached to a benzene ring -not a carbon atom- are not considered alcohols.
Aliphatic alcohols are categorized into three main classes based where hydroxyl groups are attached relative to the main alkyl group.
Primary alcohols feature a single –OH group attached to a single alkyl group. Methanol, ethanol and propanol are all examples of primary alcohols. The complexity of the alkyl chain is irrelevant to the classification of an alcohol as primary. The presence of only one linkage between the alkyl group and an –OH group is what qualifies an alcohol as primary.
Secondary alcohols feature a hydroxyl group that is connected to a carbon atom that has an alkyl group to either side. These two alkyl groups may be structurally identical or different.
Tertiary alcohols feature a hydroxyl group connected to a carbon atom that is connected to three alkyl groups. The physical properties of alcohols depend on their structure. The presence of the hydroxyl group allows alcohols to form hydrogen bonds with their neighbors. These bonds are relatively weak, but the additive effect of many bonds makes the boiling point of an alcohol much higher than its respective alkane.