BlogNCERTImportant Topic of Chemistry: Alkenes-Nomenclature

Important Topic of Chemistry: Alkenes-Nomenclature


Alkenes can be found in high concentrations in the essential oils of trees and other plants. (Essential oils are responsible for the distinctive odour, or “essence,” of the plant from which they are extracted.) Alkenes such as myrcene and limonene, for example, are found in bayberry and lime oil, respectively. The oil of turpentine is a mixture of hydrocarbons rich in -pinene that is obtained by distilling the exudate from pine trees. -Pinene is used as a paint thinner and as a starting material in the manufacture of synthetic camphor, drugs, and other chemicals. Plant pigments such as lycopene, which is responsible for the red colour of ripe tomatoes and watermelon, are examples of naturally occurring hydrocarbons with double bonds. Lycopene is a polyene (a compound with many double bonds) that belongs to the carotenes family of 40-carbon hydrocarbons.

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    The alkenes, particularly ethene, play a vital role in the chemical industry. They are not found in large quantities in crude oil but are produced by the cracking of alkanes. All hydrocarbons, including alkenes, burn in the air to produce carbon dioxide and water. As ethene reacts explosively in oxygen, it is ineffective as a fuel. Alkenes are also far too useful in the chemical industry for the production of plastics and a variety of other chemicals to be used as fuels.

    A few of the physical properties of alkenes and alkanes are similar: they are colourless, nonpolar, and combustible. The physical state is determined by molecular mass: At room temperature, gases behave similarly to the corresponding saturated hydrocarbons, the simplest alkenes, ethene, propene, and butene. The higher the boiling point, the greater the additional intermolecular mass. The intermolecular forces of alkenes become stronger as the size of the molecules increases. In each case, the boiling point of the alkene is a few degrees lower than that of the corresponding alkane.

    Also read: Important Topic of Chemistry: Inorganic Compound


    We can say that an alkene is a hydrocarbon with a carbon-carbon double bond in chemistry.

    Alkene is frequently used as a synonym for olefin, which is any hydrocarbon with one or more double bonds. Monoalkenes are classified into two types: terminal and internal. Terminal alkenes, also known as -olefins, are more useful.

    Acyclic alkenes are a homologous series of hydrocarbons with only one double bond and no other functional groups.

    Alkenes are colourless, apolar compounds that are similar to alkanes but more reactive. At room temperature, the first few members of the series are gases or liquids. The most basic alkene, ethylene (or “ethene” in IUPAC nomenclature), is the organic compound produced on a large industrial scale.

    Their general formula is CnH2n for molecules with one double bond (and no rings).

    Alkenes examples

    There are several examples for alkenes such as:

    • Ethene
    • Propene
    • 1-butene
    • 1-pentene
    • 1-heptene
    • 1-octene


    Relatively high alkenes are named by counting the number of carbons in the longest continuous chain that includes the double and adding a -ene (alkene) suffix to the stem name of the unbranched alkane with that many carbons. The chain is numbered in the direction that gives the lowest number to the first multiply bonded carbon, and this number is appended to the name as a prefix. Once the chain has been numbered in relation to the multiple bonds, the substituents attached to the parent chain are listed alphabetically and their positions are identified by number.

    Compounds with two double bonds are known as dienes, those with three as trienes, and so on. Dienes are named by replacing the corresponding alkane’s -ane suffix and identifying the positions of the double bonds with numerical locants.

    Alkene to alcohol

    In general, alkenes can be converted to alcohols by the net addition of water across the double bond. This transformation can be accomplished in a variety of ways.

    Hydration is the net addition of water to alkenes.

    Unsymmetrical alkene

    An unsymmetrical alkene is one in which the pair of ligands on one doubly bonded carbon differs from the pair on the other. An unsymmetrical alkene, like propene, has different groups or atoms attached to either end of the carbon-carbon double bond.

    Propene, for example, has a hydrogen and a methyl group at one end of the double bond but two hydrogen atoms at the other end. However, 1-ene is another asymmetrical alkene.

    Also read: Important Topic of Chemistry: pH


    What are alkenes used for?

    Alkenes have a wide range of applications in the manufacturing industry. As starting materials, they are used in the synthesis of alcohols, plastics, lacquers, detergents, and fuels. The most important alkenes in the chemical industry are ethene, propene, and 1,3-butadiene.

    Where is alkene found?

    Thermal cracking of ethane can result in the production of ethene and a hydrogen molecule. Alkenes are the raw materials for many plastics, including polyethene, PVC, polypropylene, and polystyrene. Alkene chemistry can be found in unsaturated fats, beta-carotene, and light through vision.

    Can alkenes be used as fuel?

    In contrast to alkanes, alkenes burn easily to produce carbon dioxide and water if the combustion is complete. However, for two reasons, they are NOT used as fuels. They are far too valuable for use in the production of plastics, antifreeze, and a variety of other useful compounds.

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