Organic Chemistry: Alcohols

Organic Chemistry: Alcohols

Basic Properties

  • Alcohols are a class of organic compounds that contain at least one hydroxyl group (-OH) directly bonded to a carbon atom.
  • The general formula for the simplest (primary) alcohols is CnH2n+1OH.
  • Unlike alkanes, alcohols are polar molecules because of the electronegative oxygen in the hydroxyl group.
  • This polarity allows alcohols to form hydrogen bonds, leading to higher boiling points than their corresponding alkanes.

Examples of Alcohols

  • The simplest alcohol is methanol (CH3OH), which consists of a single carbon atom bonded to three hydrogen atoms and one hydroxyl group.
  • Ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH) are all examples of primary alcohols.
  • In these examples, the n in the general formula represents the number of carbon atoms. So, for propanol, n is 3.

Nomenclature of Alcohols

  • The name of an alcohol is derived from the corresponding alkane by replacing the ‘e’ ending with ‘ol’.
  • Methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol are the names of the first 10 primary alcohols.
  • For secondary and tertiary alcohols, where the OH group is attached to a carbon atom bonded to two or three other carbon atoms respectively, the position of the hydroxyl group is indicated by a number in the name.

Structure of Alcohols

  • The OH group gives alcohols their characteristic properties. In particular, the bond between the oxygen and hydrogen atom is highly polar because oxygen is more electronegative than hydrogen.
  • As a result, alcohols are able to form hydrogen bonds with other alcohol molecules, with water, and with other polar substances.
  • Hydrogen bonding increases the boiling points of alcohols compared to alkanes of similar size, which cannot form hydrogen bonds.

Reactions of Alcohols

  • Alcohols can undergo dehydration reactions in the presence of acids to form alkenes and water.
  • Alcohols can also be oxidised to form aldehydes or carboxylic acids, depending on whether they are primary or secondary.
  • Vertically, alcohols can undergo substitution reactions, with the OH group being replaced by other atoms or groups of atoms.

Uses of Alcohols

  • Alcohols have many uses in industry, including as solvents, fuels, and as the active ingredient in alcoholic beverages. Ethanol (C2H5OH) is particularly important in these respects.
  • Alcohols are also essential for the production of a wide range of chemical products, including medicines and plastics.
  • Other uses of alcohols include antiseptics (e.g., ethanol and propanol), and antisolvents (e.g., ethanol and methanol).