Organic chemistry

The functional group in an alcohol

Importance of alcohols

The  alcohols  (alcohol function) are compounds having functional group as hydroxyl (-OH) bonded to saturated carbon in their structure.

They can have unsaturation, cyclic chains and branches. In general they are soluble in water and up to eleven carbons are liquid.

Alcohols can be considered weak acids because, as oxygen is very electronegative, it attracts electrons from the bond to itself and leaves hydrogen with an acidic character.

This makes the alcohols capable of carrying out various reactions.

General formula of alcohols:  R-OH

Content Index

  • 1 Features
  • 2 Classification
  • 3 Nomenclature of alcohols
  • 4 Importance
  • 5 Examples of important alcohols
    • 5.1 Methyl alcohol (methanol)
    • 5.2 Ethyl alcohol (ethanol)
    • 5.3 Cholesterol

Features of alcohols

  • They are organic compounds.
  • They present the -OH group attached to the carbon chain.
  • They are colorless .
  • They have high melting and boiling points.
  • Alcohols have a polar and a non-polar part in the molecule.
  • Alcohols whose chain is short are water soluble (chains with less than 4 carbons).
  • The long-chain ones are insoluble in water (4-carbon chains onwards).
  • They are liquid if the chain is short (up to 11 carbon atoms) and solid if the chain is long (12 or more carbon atoms).
  • They are classified into primary, secondary and tertiary alcohols.

Classification of alcohols

The alcohols can be classified according to the number of hydroxyl groups present in the structure:

  • A hydroxyl:  monoalcohol
  • Two hydroxyls:  dialcohol
  • More than three hydroxyls:  polyalcohol

Another way of classifying alcohols is according to the type of carbon attached to the hydroxyl:

  • Primary Carbon:  Primary Alcohol
  • Secondary carbon:  secondary alcohol
  • Tertiary Carbon:  Tertiary Alcohol

Nomenclature of alcohols

Prefix + link type +  OL

As in the alcohols there is the presence of a functional group, the main chain count must start at the nearest end of the hydroxyl.

In structures that have more than one hydroxyl group, the count must be the one that provides the lowest numbering for these groups and the prefixes di, tri, tetra should be used to designate the amount of hydroxyl.

In branched chains, the IUPAC rules apply  , with the main chain count being the one containing the branch with the lowest hydroxyl numbering.

In unsaturated alcohols, their names must include the positions of the functional group, the unsaturations and the branches, this being the order of priority.

In the case of monoalcohols, there is the possibility of using a customary nomenclature, in which the radical attached to the hydroxyl group is called following the prefixes and using the IOL termination.

Importance of alcohols 

The alcohols comprise organic molecules with a hydroxyl group (OH) in their composition.

Thus, its use in human activities is diverse and can be  used in the manufacture of cosmetics and perfumes , in glycerin for  industrial activities , in the process of  production of alcoholic beverages , in the food sectors (sugar production) and in the formation of Cellulose, which will be used for the manufacture of newspapers.

Examples of important alcohols

Methyl alcohol (methanol)

Methanol (CH3OH) is an invisible flammable liquid, widely used in cars of Indy formula. Due to the characteristics of its flame, the work teams in the area receive special training to avoid accidents.

Its manipulation requires special care and caution in contact with the skin, since methanol causes irritation of the mucous membranes, having a more aggressive effect on the nervous system.

Ethyl alcohol (ethanol)

Ethanol (C2H5OH) is widely used as fuel, mainly in the most tropical countries, due to its low operating temperature and clean combustion compared to gasoline and diesel, as it does not release sulfur compounds into the atmosphere.

In Brazil, it is obtained by fermenting mainly sugar cane, but it can be obtained from several other sources.


Cholesterol (C27H45OH) is a steroid that forms the cell membranes of all mammals and is transported by blood plasma.

It is a long-chain polycyclic alcohol, insoluble in water and blood, so when transported it binds to water-soluble proteins.


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