Alcohol

In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). This sense underlies the term alcoholism (addiction to alcohol). Other forms of alcohol are usually described with a clarifying adjective, as in isopropyl alcohol or by the suffix -ol, as in isopropanol.

Physical and chemical properties

The hydroxyl group generally makes the alcohol molecule polar. Those groups can form hydrogen bonds to one another and to other compounds. Two opposing solubility trends in alcohols are: the tendency of the polar OH to promote solubility in water, and of the carbon chain to resist it. Thus, methanol, ethanol, and propanol are miscible in water because the hydroxyl group wins out over the short carbon chain. Butanol, with a four-carbon chain, is moderately soluble because of a balance between the two trends. Alcohols of five or more carbons (Pentanol and higher) are effectively insoluble because of the hydrocarbon chain's dominance.

Related Topics:
Hydroxyl group - Polar - Hydrogen bond - Butanol - Pentanol

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Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. All simple alcohols are miscible in organic solvents. This hydrogen bonding means that alcohols can be used as protic solvents.

Related Topics:
Hydrogen bonding - Hydrocarbon - Ether - Protic solvent

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The lone pairs of electrons on the oxygen of the hydroxyl group also makes alcohols nucleophiles.

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Alcohols, like water, can show either acidic or basic properties at the O-H group. With a pKa of around 16-19 they are generally slightly weaker acids than water, but they are still able to react with strong bases such as sodium hydride or reactive metals such as sodium. The salts that result are called alkoxides, with the general formula RO- M+. Meanwhile the oxygen atom has lone pairs of nonbonded electrons that render it weakly basic in the presence of strong acids such as sulfuric acid. For example, with methanol:

Related Topics:
PK_a - Acid - Water - Sodium hydride - Sodium - Alkoxide - R - M - Lone pair - Basic - Sulfuric acid

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Alcohols can also undergo oxidation to give aldehydes, ketones or carboxylic acids, or they can be dehydrated to alkenes. They can react to form ester compounds, and they can (if activated first) undergo nucleophilic substitution reactions. For more details see the #Chemistry of alcohols section below.

Related Topics:
Oxidation - Aldehyde - Ketone - Carboxylic acid - Alkene - Ester compound - Nucleophilic substitution - #Chemistry of alcohols

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