One of the class of organic molecules containing an alkyl group connected to a hydroxyl group, ROH. The archetypal example ethanol, CH3CH2OH, is also commonly referred to simply as ‘alcohol’. A dihydric alcohol has two hydroxyl groups; polyhydric alcohol. The physical properties of alcohols depend on the hydrogen bonding between the hydroxyl groups of neighbouring molecules; for example, their boiling points are significantly higher than those of the corresponding isomeric ethers. They react with chlorinating agents to form chloroalkanes, and with acids to form esters. They can be dehydrated by concentrated sulfuric acid to alkenes. The oxidation product of an alcohol depends on the structure of the alkyl group. A primary alcohol has two hydrogen atoms on the neighbouring carbon atom (next to the hydroxyl group): primary alcohols are oxidized to aldehydes and thence to carboxylic acids. A secondary alcohol has only one hydrogen atom on the neighbouring carbon atom: secondary alcohols are oxidized to ketones. A tertiary alcohol has no hydrogen atoms on the neighbouring carbon atom: tertiary alcohols resist oxidation (see the diagram). Ethanol is by far the most important alcohol; it is used in alcoholic drinks, as an industrial solvent and in the manufacture of ethanoic acid. Methanol is used as a fuel. Higher alcohols are used to manufacture detergents and plasticizers.
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