organic chemistry

• Originally, organic chemistry referred to compounds obtained from plants or animals
• Modern definition: organic compounds contain carbon as their essential constituent
• Carbon atom has 4 electrons in the outermost shell, shares valence electrons to form covalent bonds
• Tetravalency of carbon: carbon atom can form 4 covalent bonds
• Catenation: self-linking capacity of carbon atoms to form giant molecules
• Organic compounds can form long chains or rings: straight chain, branched chain, closed chain
• Cyclic compounds contain rings of atoms, aliphatic compounds are open chain
• Characteristics of Organic Compounds:

  • Covalent nature
  • Insoluble in water, soluble in organic solvents
  • Low melting and boiling points compared to inorganic compounds
  • Exhibit isomerism
  • Burn in air to produce carbon dioxide and water
• Isomerism: compounds with the same molecular formula but different structures
• Functional group: atom or group of atoms defining properties of organic compounds
• Homologous series: group of organic compounds with similar structures and properties, differing by CH2 group
• Hydrocarbons: compounds containing only hydrogen and carbon
• Alkanes:

  • Hydrocarbons with no multiple bonds
  • General formula: CnH2n+2
  • Methane, ethane, propane, butane are examples
  • Show isomerism
• Alkenes:

  • Unsaturated hydrocarbons with carbon-carbon double bond
  • General formula: CnH2n
  • Ethene, propene are examples
• Alkynes:

  • Unsaturated hydrocarbons with carbon-carbon triple bond
  • General formula: CnH2n-2
  • Ethyne, propyne are examples
• Alcohols:

  • General formula: CnH2n+1OH
  • Named as alkanols in IUPAC system
  • Methanol, ethanol, propanol are examples
• Aldehydes:

  • General formula: CnH2n+1CHO
  • Named by replacing 'e' of alkane with 'al'
  • Formaldehyde, acetaldehyde, propionaldehyde are examples
• Carboxylic Acids:

  • General formula: R—COOH
  • Classified as monocarboxylic, dicarboxylic acids, etc.
  • Named by replacing 'e' of alkane with 'oic acid'
  • Methanoic acid, ethanoic acid, propanoic acid are examples
• Methane:

  • First member of alkanes
  • Tetrahedral structure
  • Occurs in marshy lands, coal mines, natural gas
  • Prepared by heating sodium acetate with soda lime or reduction of methyl iodide
• Physical Properties of Methane:

  • Colourless, odourless, tasteless, non-poisonous gas
  • Boiling point: -164°C, melting point: -184°C
  • Sparingly soluble in water, soluble in organic solvents
  • Lighter than air, vapour density: 8
• Chemical Properties of Methane:

  • Burns in excess air to form CO2 and water
  • Burns in limited air to form CO and water
  • Reacts with steam in presence of nickel catalyst to form CO and H2
  • Oxidation with potassium dichromate produces alcohol, aldehyde, acid
  • Undergoes substitution reactions with chlorine
  • Decomposes into carbon and hydrogen at high temperatures
  • Decomposes into acetylene at very high temperatures
• Uses of Methane:

  • Domestic fuel
  • Making carbon black
  • Fuel in automobiles
  • Making chloroform
• Methane (CH4)

  • Uses:
  • Used as a domestic fuel
  • Used for making carbon black
  • Used in automobiles as a fuel
  • Used for making chloroform by regulated chlorination
  • Used for manufacturing methanol, formaldehyde, etc.
• Ethane (C2H6)

  • Occurrence:
  • Second member of the homologous series of alkanes
  • Occurs in mineral oil and natural gas
  • Preparation:
  • Prepared by heating sodium propionate with soda lime
  • Also prepared by the reduction of ethyl iodide
• Ethene or Ethylene (C2H4)

  • Preparation:
  • Prepared by dehydration of ethanol
  • Also prepared by dehydrohalogenation of ethyl chloride with alcoholic potassium hydroxide
  • Uses:
  • Used for the manufacture of detergents
  • Used for artificial ripening and preservation of fruits
  • Used as general anaesthesia
  • Used in the manufacture of synthetic chemicals
  • Used in the manufacture of polymers
• Acetylene or Ethyne (C2H2)

  • Preparation:
  • Prepared by the action of water on calcium carbide
  • Can also be prepared by boiling ethylene dibromide with alcoholic potassium hydroxide solution
  • Uses:
  • Used for illumination, especially in acetylene lamps
  • Used in the production of oxy-acetylene flame for cutting and welding
  • Used for artificial ripening of fruits
  • Used in the manufacture of organic compounds
  • Used as a starting material to prepare plastics, synthetic rubber, etc.
• Ethanol or Ethyl alcohol (C2H5OH)

  • Preparation:
  • Prepared by ethene
  • Also prepared by hydrolysis of ethyl halides
  • Uses:
  • Used in the manufacture of beer, wine, and other alcoholic beverages
  • Used as a solvent for paints, varnishes, oils, and dyes
  • Used as a fuel
  • Used in the synthesis of many organic compounds
• Acetic Acid or Ethanoic Acid (CH3COOH)

  • Preparation:
  • From ethanol by oxidation with bacterium acetii
  • Uses:
  • Used in the manufacture of white vinegar, acetone, esters, pharmaceuticals, drugs, dyes, perfumes, cellulose, acetate, polyvinyl acetate, and metal acetate
  • Used as a laboratory reagent