In general alcohols are any of the class of organic compouns that consist of a hydroxyl group (-OH) attached to a hydrocarbon. For example, the simplest two alcohols are methanol and ethanol (also called methyl alcohol and ethyl alcohol, respectively), which have the following structures:
H H H | | | H-C-O-H H-C-C-O-H | | | H H H
In common usage alcohol refers simply to ethanol, which may be produced by fermentation of fruits or grains with yeast, and is one of the oldest and most widely used recreational drugs in the world, typically taken in the form of a drink. Ingestion in sufficient quantity results in a state known as drunkenness.
Other notable alcohols are isopropyl alcohol (2-propanol), which is present in rubbing alcohol, and ethylene glycol, which is the primary component in antifreeze. Except for ethanol, alcohols are very hazardous when ingested - for instance methanol causes blindness - and can be created in uncontrolled fermentation processes. Alcohols are in wide use in the industry and science fields as reagents, solvents, and fuels. State-of-the-art engineering has achieved replacement of gasoline (and other hydrocarbons which produce toxic fumes) with forms of alcohol such as ethanol or methanol (which burn more cleanly).
The hydroxyl groups in alcohols are capable of forming hydrogen bonds to one another and to other compounds. Because of this alcohols tend to have higher boiling points than comparable hydrocarbons and ethers, and the smaller ones tend to be very or completely miscible with water. Alcohols are very weak acids, except for methanol being weaker than water, but still stronger than ammonia or acetylene. They burn fairly readily.
One important class of reactions undergone by alcohols are nucleophilic substitutions, where one nucleophilic group attached to a carbon atom is replaced by another. So, for instance, alcohols will react with hydrochloric acid to produce alkyl halides, where the hydroxyl group being replaced by a chlorine atom. The equilibrium here lies to the right, since chlorine is a stronger nucleophile, but can be driven to the left using an alkaline medium, and this is one way of synthesizing alcohols.
Actually, alcohols are themselves nucleophilic, so can react with one another to produce ethers and water. They will also react with hydroxy acids (or acid halides) to produce compounds called esters, of which the esters of organic acids are the most important. Under high temperatures, alcohols can under go an elimination reaction to produce alkenes. The reverse of this, the addition of water to an alkene to produce an alcohol, is catalyzed by acids but is of limited use for synthesis because it generally results in mixtures. Some other techniques exist to convert alkenes to alcohols more reliably.