Organic compound

  • The compounds of mainly carbon and hydrogen or compounds of carbon and hydrogen with other elements like phosphorous, oxygen, nitrogen, sulphur, halogens etc which are called organic compounds
  • Organic compounds are divided into two types namely open-chain compounds and cyclic compounds
  • Open chain compounds can be divided into saturated compounds and unsaturated compounds
  • The cyclic compounds are divided into homocyclic compounds and heterocyclic compounds
  • The homocyclic compounds are divided into alicyclic compounds (eg: cyclohexane) and aromatic compounds (eg: benzene)
  • The heterocyclic compounds are divided into alicyclic compounds (e.g.: epoxy ethane) and aromatic compounds (e.g.: furan)

Berzelius hypothesis/ vital force theory

  • It was thought that organic compounds cannot be synthesised in laboratories because they require the presence of vital force which exists only in the living organisms
  • Urea is the first organic compound prepared in a laboratory
  • Urea was prepared by Wohler in 1828 from an inorganic compound ammonium cyanate
  • Acetic acid was the first organic compound synthesised from the elements by Kolbe
  • Functional group: it is an atom in a group of atoms in a molecule, which is responsible for the chemical properties of the molecule. -OH is an alcoholic group, ­-CHO is aldehyde group, >C=O is keto group, -COOH is carboxyl group, –O—is ether group
  • Homologue’s series: it is a series of compounds in which adjacent members differ by a      –CH2 unit (14-unit mass)
  • Isomers: compounds having the same molecular formula but different structural formula e.g.: dimethyl ether and ethanol

Hydrocarbons:

  • These are the compounds of only carbon and hydrogen they are divided into three types saturated hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons
  • Saturated hydrocarbons: they contain only single bonds. They are also called alkanes or paraffin and have a general formula CnH2n+2 where n=1,2,3. Methane is the first member of the group
  • Unsaturated hydrocarbons: they have the general formula CnH2n for alkene and CnH2n-2 for alkynes. These have at least one double or tribble bond and are called alkenes and alkynes respectively
  • Aromatic hydrocarbons: they have a ring structure with alternate double bonds and huckle’s rule

Important hydrocarbons and their uses

Methane (CH4):

  •  it is a colourless, odourless gas.
  •  It is also known as marsh gas or damp fire.
  •  Natural gas contains mainly 90% methane along with ethane, propane, butane etc. rice agriculture is a big source of atmospheric methane.
  •  Its mixture with air is explosive
  • It is the cause of occurrence of the explosion in mines
  • It is used as a fuel gas in making carbon black, various organic compounds and in the various industrial preparation

Biogas:

  • It is a mixture of gases produced during the decay of biomass in the absence of oxygen
  • Methane (75%) is the main constituent of biogas
  • It is an excellent fuel and burns without producing smoke

Ethane (C2H6):

  • Natural gas contains approx. 10% ethane
  • It is used as a fuel and in making some organic compounds
  • Its hexachloro derivative C2CL6 is used as an artificial camphor

Butane (C4H10):

  • It is the main constituent of LPG
  • It is also present in small amount in natural gas
  • It is used as a fuel

Ethylene (CH2=CH2):

  • In world war I (1914-1981), it was used for the manufacturing of mustard gas (a poisonous gas)
  • It is used as an anaesthetic for the preservation and artificial ripening of green fruits and also used in the manufacturing of ethyl alcohol, ethylene glycol, polythene and polyvinyl chloride (PVC) etc

Acetylene (CH=CH):

  • A colourless gas with a sweet smell
  • The characteristic odour associated with acetylene is due to phosphine present as an impurity
  • It is dangerously explosive in a liquid state, so its use or storage is prohibited by law
  • It is used in oxy- acetylene blowpipe as an illuminate for artificial ripening of fruits, in the manufacturing of solvents such as westron and wester sol
  • Several polymers such as plastics, synthetic rubber and synthetic fibre are obtained by acetylene

Benzene (C6H6):

  • It is the simplest aromatic hydrocarbon
  • It was discovered by Faraday in 1825
  • He obtained it by the destructive distillation of white oil
  • It is used as a solvent for fats, resins etc it is also used as a motor fuel under the name benzol

Toluene(C6H5CH3):

  • It was first obtained by the dry distillation of tolu balsam
  • It is used as a commercial solvent in the manufacturing of explosive (TNT) drugs, (chloramine-T) and dyestuff
  • It finds use in the manufacturing of saccharin and print inking inks, with petrol and benzene, toluene is used as antifreeze

Xylene(C8H10):

  • It is used in the manufacturing of lacquers and as solvents of rubber

Naphthalene(C10H8):

  • It constitutes about 6-10% of coal tar
  • It is a colourless crystalline solid with a strong characteristic odour
  • It is used for preventing moths in cloths, as an insecticide and in the manufacturing of azodyes, eosin, indigo

Halogen derivatives of hydrocarbons

     Ethyl bromide (C2H5Br):

  • It is a colourless, pleasant smelling liquid
  • It is used as a local anaesthetic and in organic synthesis

Chloroform (CHCl3)

  • It was discovered by Liebig in 1831
  • It is a colourless, mobile liquid with a sweet sickly odour and taste
  • It is stored in closed dark coloured bottles filled because it is oxidised by air in the presence of sunlight to form an extremely poisonous gas phosgene
  • It reacts with conc. HNO3 and form chloropicrin (Cl3C—NO2)
  • Chloropicrin (Cl3C—NO2) is an insecticide and also used as poisonous gas at the time of war
  • It is used as a solvent for fats. Alkaloids, iodine and other substances
  • The major use of chloroform today is in the production of the freon refrigerant
  • It is used as a general anaesthetic in surgery but has been replaced by less toxic either
  • Chronic chloroform exposure may cause damage to the liver and kidneys

Iodoform (CHI3)

  • It is a pale yellow crystalline solid with a characteristic unpleasant odour
  • It is insoluble in water but soluble in ethyl alcohol and ether
  • It is used as an antiseptic due to the liberation of free iodine

Carbon tetrachloride (CCl4)

  • It is a colourless, heavy liquid
  • It is extensively used as an industrial solvent for fats, oils, resins, lacquers and as a fire extinguisher under the name pyrene

Freon

  • The chloroform carbon compounds of methane and ethane are collectively known as ferons
  • These are usually produced for aerosol propellants, refrigeration and air-conditioning purpose
  • In the stratosphere, ferons can upset the natural ozone balance

Dichloro diphenyl trichloroethane (DDT):

  • It was the first chlorinated organic insecticides and originally prepared in 1873
  • The effectiveness of DDT as an insecticide was discovered by Paul muller and he was awarded the Nobel prize in medicine and physiology in 1948
  • It is highly stable and is not easily decomposed

Benzene hexachloride (BHC):

  • The trade name of BHC is lindane and gammaxene
  • It is prepared by the addition of chlorine to benzene in the presence of ultraviolet rays
  • Used as a pesticide in agriculture

Chlorobenzene(C6H5CL):

  • It is a colourless, pleasant smelling liquid used for manufacturing phenol, aniline and DDT
  • Chlorobenzene on heating with chloral in the presence of conc. H2SO4 gives DDT

p-Dichloro benzene(C6H4Cl2):

  • It is a white volatile solid, readily sublimes
  • It is used as a general insecticide, germicide, soil fumigant, deodorant and moth repellent

Perfluorocarbons (PFC’S):

  • These are non-toxic, non-flammable, non-corrosive, extremely stale and unreactive gasses, liquids or solids
  • These are used as electrical insulators, lubricants, dielectrics, heat transfer media in high voltage electrical equipment
  • They find several applications in health, care and medicine

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