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These are compounds containing at least one triple bond between any two successive carbon atoms. They are also known as acetylenes. They form a series of homologous compounds with the general formula CnH2n-2, where n = 2, 3, 4, etc. The names of the members of the alkyne series are obtained by substituting ‘yne’ in place of ‘ane’ in alkanes.

Preparation of Alkynes

  1. Ethyne is prepared when electric arc is struck between carbon electrodes in the atmosphere of hydrogen.
    2C + H2 Description: 39369.jpg C2 H2
  2. From dehalogenation reaction: Dehalogenation of alkyl halide gives alkynes.
    1,1,2,2-Tetrabromoethane when heated with zinc gives acetylene (ethyne).
    Description: 31734.png
        Elimination reaction 
  3. From alkyl dihalides: Dehydrohalogenation of alkyl halide gives alkynes.
    1,2-Dibromoethane when heated with alcoholic potassium hydroxide gives ethyne.
    Description: 31743.png
Chemical Reactions
  1.  Description: 34113.png
  • Chlorination
  • Electrophilic
  1. Description: 31779.png
  • Hydrohalogenation
  • Electrophilic
Hydrocarbons are further classified based on the special group or more reactive groups attached to it. This special group governs the chemical reactivity of the compound. Such a group is called a ‘functional group’. Hydrocarbons having such a functional group are called derivatives of hydrocarbons. Some functional groups present in the organic compounds are given in Table.


Functional Groups in Their Respective Organic Compounds



Functional Groups

Found in Nature




When fruits and vegetables ferment

Used as dehydrating agents, fuel, beverage.



In cherries

Used as formalin to preserve biological specimens.


In camphor

Used as a solvent for resins lacquers, and cellulose. In perfumes, and in making flavourings, dyes etc.

Acid (carboxylic acid)


In the form of organic acids—vinegar, oxalic acid, citric acid etc.

Used as food preservatives, good dehydrating agents

Halogen compounds

–X (Cl, Br, I)

Used in the form of DDT, Freons, organic solvents

Nitro compounds


In termites for defence purpose

Used in explosives (TNT, picric acid etc.)



In living organisms in the form of protein linkages

Used in the pharmaceutical industry, paper, plastic industry.



Used as local anaesthetic agents.



Smell of fruits is because of esters

Different salts of esters are used in the preparation of soaps. As solvents, in
making flavours, essence and artificial
food colouring.



Used in dyes, drugs etc.

  1. Isomerism: It is a phenomenon in which two or more organic compounds have the same molecular formula but differ in their physical and chemical properties, e.g. CH3CH2OH (ethanol) and CH3-O-CH3 (dimethylether).

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