In common usage the term alcohol usually refers to ethanol . An alcohol is generally classified by the number of hydroxyl groups in its molecule.
Glycols have two hydroxyl groups in their molecules and so are dihydric.
Glycerol, with three hydroxyl groups, is trihydric. The monohydric alcohols are further classified as primary, secondary, or tertiary according to the number of carbon atoms bonded to the carbon atom to which the hydroxyl group is bonded. For example, at room temperature methanol is a liquid, while methane is a gas. Listing from Electric Library , a pay service. Copyright 2001 Infonautics Corporation .