Functional Or Characteristic Group

Hydrocarbons are the parent organic compounds.All other compounds are considered to have been derived from them by replacing one or more of their hydrogen atoms by some other more reactive atom or group.

R—H ——–> R—G

-H and +G

Each organic molecule consist of two parts i.e. R and G.

The first part, i.e. R denotes the carbon -hydrogen framework of the molecule while the second part i.e. G is called the functional group.

A functional group may be defined as as atom or a group of atoms present in a molecule which largely determines its chemical properties.

The remaining part of a molecule mainly affects the physical properties such as melting point, boiling point , density, solubility, refractive index etc.

The chemical properties of any organic compound are the properties of its functional group.

All the organic compounds containing the same functional group show similar chemical reactions.

Class of organic compounds Name of the functional group


Structure of the functional group
Alkenes Double bond  alkene
Alkynes Triple bond  alkyne
Halogen derivative Halogen  —X (F, Cl, Br, I)
Alcohols Hydroxy  —OH
Thioalcohol Thiols  —SH
Ethers Divalent oxygen  —O—
Thioethers Divalent sulphur  —S—
Aldehydes Aldehydic  aldehyde
Ketones Thiol  ketone
Thioketones Thione Thioketone
Carboxylic acid Carboxyl  carboxylic acid
Acid chlorides Chlorocarbonyl  acid chloride
Acid anhydride Anhydride  acid anhydride
Esters Alkoxycarbonyl  Ester group
Acid amide Amide  Acid amide group
Sulphonic acid Sulphonic acid  Sulphonic acid group
Primary amines Amino  Amino
Secondary amines Imino  Imino group
Tertiary amines Tertiary -N- atom  Tertiary amine
Alkyl cyanide Cyano or nitrile  Cyano group
Alkyl isocyanide Isonitrile  Isonitrile group
Nitroalkanes Nitro  Nitro group
Alkyl nitrites Nitrite  Nitrite group
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