About Alcohol
In chemistry, an alcohol is any organic compound in which a hydroxyl functional group is bound to a carbon atom, usually connected to other carbon or hydrogen atoms.
An important class are the simple acyclic alcohols, the general formula for which is CnH2n+1OH. Of those, ethanol is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol refers specifically to ethanol.
Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol or wood alcohol . The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; in substances where a higher priority group is present the prefix hydroxy- will appear in the IUPAC name. The suffix -ol in non-systematic names also typically indicates that the substance includes a hydroxyl functional group and so can be termed an alcohol, but many susbtances contain one or more hydroxyl functional groups without using the suffix.
The most commonly used alcohol is ethanol, C2H5OH, with the ethane backbone. Ethanol has been produced and consumed by humans for millennia, in the form of fermented and distilled alcoholic beverages. It is a clear flammable liquid that boils at 78.4 °C, which is used as an industrial solvent, car fuel, and raw material in the chemical industry. In the US and some other countries, because of legal and tax restrictions on alcohol consumption, ethanol destined for other uses often contains additives that make it unpalatable or poisonous . Ethanol in this form is known generally as denatured alcohol; when methanol is used, it may be referred to as methylated spirits or "surgical spirits".
The simplest alcohol is methanol, CH3OH, which was formerly obtained by the distillation of wood and therefore is called "wood alcohol". It is a clear liquid resembling ethanol in smell and properties, with a slightly lower boiling point , and is used mainly as a solvent, fuel, and raw material. Unlike ethanol, methanol is extremely toxic: one sip can cause permanent blindness by destruction of the optic nerve and 30 ml is potentially fatal.
Two other alcohols whose uses are relatively widespread are propanol and butanol. Like ethanol, they can be produced by fermentation processes. Saccharomyces yeast are known to produce these higher alcohols at temperatures above 75 F. These alcohols are called fusel alcohols or fusel oils in brewing and tend to have a spicy or peppery flavor. They are considered a fault in most styles of beer.
Simple alcohols, particularly ethanol and methanol, possess denaturing and inert rendering properties, leading to their use as anti-microbial agents in medicine, pharmacy and industry.
In the IUPAC system, the name of the alkane chain loses the terminal "e" and adds "ol", e.g. "methanol" and "ethanol". When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the "ol": propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CHCH3. Sometimes, the position number is written before the IUPAC name: 1-propanol and 2-propanol. If a higher priority group is present , then it is necessary to use the prefix "hydroxy", for example: 1-hydroxy-2-propanone .
The IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important. In other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word "alcohol", e.g. methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol depending on whether the hydroxyl group is bonded to the 1st or 2nd carbon on the propane chain.
Alcohols are classified into primary, secondary and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl group. Namely, the primary alcohols have general formulas RCH2OH; secondary ones are RR'CHOH; and tertiary ones are RR'R"COH, where R, R' and R" stand for alkyl groups. Ethanol and n-propyl alcohol are primary alcohols; isopropyl alcohol is a secondary one. The prefixes sec- and tert- , conventionally in italics, may be used before the alkyl group's name to distinguish secondary and tertiary alcohols, respectively, from the primary one. For example, isopropyl alcohol is occasionally called sec-propyl alcohol, and the tertiary alcohol 3COH, or 2-methylpropan-2-ol in IUPAC nomenclature, is commonly known as tert-butyl alcohol or tert-butanol.