Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is CnH2n+1OH. Of those, ethanol (C2H5OH) is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol means, specifically, ethanol.

Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol (propan-2-ol) or wood alcohol (methyl alcohol, or methanol). The suffix -ol appears in the IUPAC chemical name of all alcohols.

There are three major subsets of alcohols: primary (1°), secondary (2°) and tertiary (3°), based upon the number of carbon atoms the C-OH group’s carbon (shown in red) is bonded to. Ethanol is a simple ‘primary’ alcohol. The simplest secondary alcohol is isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is tert-butyl alcohol (2-methylpropan-2-ol).

Simple alcohols

The simplest and most commonly used alcohols are methanol and ethanol. Methanol was formerly obtained by the distillation of wood and called “wood alcohol.”

One sip of methanol (as little as 10 mL) can cause permanent blindness by destruction of the optic nerve and 30 mL is potentially fatal.

Apart from its familiar role in alcoholic beverages, ethanol is also used as a highly controlled industrial solvent and raw material. To avoid the high taxes on ethanol for consumption, additives are added to make it unpalatable (such as denatonium benzoate—”Bitrex”) or poisonous (such as methanol). Ethanol in this form is known generally as denatured alcohol; when methanol is used, it may be referred to as methylated spirits (”Meths”) or “surgical spirits”.

Two other alcohols whose uses are relatively widespread (though not so much as those of methanol and ethanol) are propanol and butanol. Like ethanol, they can be produced by fermentation processes. (However, the fermenting agent is a bacterium, Clostridium acetobutylicum, that feeds on cellulose, not sugars like the Saccharomyces yeast that produces ethanol.)

Isopropyl alcohol

Isopropyl alcohol is a common name for a colorless, flammable chemical compound with a strong odor. It has the molecular formula C3H7OH and is the simplest example of a secondary alcohol, where the alcohol carbon is attached to two other carbons. It is an isomer of propanol. The name “isopropanol” is sometimes used but this is, strictly speaking, incorrect as it uses elements from two scientific naming conventions.

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