𧬠Chemistry — Organic Chemistry
1. Introduction to Organic Chemistry
DEFINITION
- Compounds of carbon and hydrogen or carbon with other elements (O, N, S, P, halogens)
- Vital Force Theory: Believed organic compounds could not be synthesised in lab
- First organic compound synthesised: Urea by WΓΆhler (1828) from NH₄CNO
- First organic compound from elements: Acetic acid by Kolbe
KEY CONCEPTS
- Functional group: Atom/group responsible for chemical properties (e.g., OH, CHO, COOH)
- Homologous series: Compounds differing by CH₂ unit; same functional group, similar properties
- Isomers: Same molecular formula, different structures (e.g., C₂H₆O → ethanol & dimethyl ether)
2. Hydrocarbons
SATURATED HYDROCARBONS (Alkanes)
- Only single bonds (C-C)
- General formula: CβH₂β₊₂
- Also called paraffins
- Methane (CH₄): Marsh gas, damp fire; 90% of natural gas
- Biogas: 75% methane; produced by biomass decay
- Butane (C₄H₁₀): Main constituent of LPG
UNSATURATED HYDROCARBONS
- Alkenes: CβH₂β (double bond) — e.g., Ethylene (C₂H₄)
- Alkynes: CβH₂β₋₂ (triple bond) — e.g., Acetylene (C₂H₂)
- Ethylene: Used for artificial ripening of fruits, anaesthetic
- Acetylene: Used in oxy-acetylene welding, artificial ripening
AROMATIC HYDROCARBONS
- Ring structure with alternate double bonds
- Benzene (C₆H₆): Discovered by Faraday (1825); used as solvent (benzol)
- Toluene (C₆H₅CH₃): Used in TNT explosives, drugs, saccharin
- Naphthalene (C₁₀H₈): 6-10% of coal tar; used as moth repellent, insecticide
3. Halogen Derivatives
IMPORTANT COMPOUNDS
- Chloroform (CHCl₃): Stored in dark bottles; oxidises to phosgene (COCl₂) in sunlight
- Iodoform (CHI₃): Pale yellow solid; antiseptic (liberates iodine)
- Carbon tetrachloride (CCl₄): Fire extinguisher (Pyrene); industrial solvent
- Freons: CFCs; used as refrigerants, aerosol propellants; deplete ozone layer
- DDT: Chlorinated insecticide; discovered by Paul Muller (Nobel 1948); banned in many countries
- BHC (Lindane, Gammaxane): Pesticide; prepared by chlorination of benzene
4. Oxygen-Containing Compounds
ALCOHOLS
- Methyl alcohol (CH₃OH): Wood spirit; poisonous (causes blindness); used as solvent, antifreeze
- Ethyl alcohol (C₂H₅OH): Grain alcohol; used in beverages, solvents
- Ethylene glycol (CH₂OH·CH₂OH): Antifreeze in automobiles
- Glycerol (C₃H₅(OH)₃): Hygroscopic; used in cosmetics, lubricants, nitroglycerine (explosive)
- Phenol (C₆H₅OH): Carbolic acid; antiseptic; used in bakelite, aspirin, picric acid
ALDEHYDES & KETONES
- Formaldehyde (HCHO): 40% solution = Formalin; antiseptic, preservative; used in bakelite
- Acetaldehyde (CH₃CHO): Used in silvering mirrors, paraldehyde (hypnotic)
- Chloral (CCl₃CHO): Used in DDT production; chloral hydrate = hypnotic
CARBOXYLIC ACIDS & ESTERS
- Acetic acid (CH₃COOH): Vinegar (6-10%); used in dyes, pharmaceuticals
- Esters: Fruity smell; used in perfumes and flavouring agents
5. Nitrogen-Containing Compounds
AMINES & NITRO COMPOUNDS
- Aniline (C₆H₅NH₂): Used in dyes, drugs, rubber vulcanisation
- Nitrobenzene (C₆H₅NO₂): Oil of mirbane; used in aniline production, perfumes
- TNT (Trinitrotoluene): Pale yellow crystalline solid; explosive
- Urea (NH₂CONH₂): First organic compound synthesised (WΓΆhler); final protein decomposition product
- Methyl isocyanate (MIC): Bhopal gas tragedy (1984); used in insecticide production
6. Bioactive Compounds
ALKALOIDS
- Nitrogenous compounds of vegetable origin
- Nicotine: Tobacco (0.6-8%); very poisonous
- Quinine: Cinchona bark; kills malaria-causing microorganisms
- Morphine: Opium from poppy; used as pain reliever
- Reserpine: Rauwolfia serpentina; used for blood pressure
TERPENES & OTHER COMPOUNDS
- Menthol: Oil of peppermint; antiseptic, in ointments
- Camphor: Moth repellent, preservative in cosmetics
- Carotenoids: Ξ²-carotene in carrots; Vitamin-A derivative
- Steroids: Cholesterol, Vitamin D, hormones
- Flavonoids: Antioxidants; responsible for flower colouration
7. Coal and Petroleum
COAL
- Fossil fuel formed by carbonisation of vegetable matter
- Types: Anthracite (90% C), Bituminous (70% C), Lignite (40% C), Peat (10-15% C)
- Destructive distillation: Coke (solid residue), Coal tar, Coal gas
- Indian coal: High ash content, low sulphur
PETROLEUM
- Fossil fuel; mixture of hydrocarbons
- First oil well: Pennsylvania, USA (1859); First in India: Makum, Assam (1867)
- Found in: Assam, Mumbai High, Gujarat, Godavari/Krishna basins
- Brent crude: Sweet light crude oil benchmark; extracted from North Sea
- Refining: Fractional distillation separates fractions
PETROLEUM FRACTIONS
| Fraction | Composition | Uses |
|---|---|---|
| Petroleum gas | C₁-C₄ | Fuel gas, LPG |
| Petrol | C₅-C₁₀ | Motor fuel |
| Kerosene | C₁₀-C₁₃ | Fuel, oil gas |
| Diesel | C₁₃-C₁₈ | Diesel engines |
| Lubricating oil | C₁₅-C₁₈ | Lubrication |
| Paraffin wax | C₁₈-C₃₀ | Ointments, candles |
FUEL PROPERTIES
- Knocking: Pre-ignition in petrol engine; reduced by antiknock compounds (TEL, BTX)
- Octane number: Measure of antiknocking property; higher = better quality
- LPG: Propane + Butane; used as household fuel
- CNG: Compressed Natural Gas; octane rating 130; less polluting
- Gasohol: 10% ethanol + 90% petrol; environmental friendly
- Calorific value (kJ/g): Hydrogen (150) > Methane (55) > Butane (55) > Petrol (48) > Wood (17)
Summary: Organic Chemistry at a Glance
| Topic | Key Point |
|---|---|
| First Organic Compound | Urea by WΓΆhler (1828) from NH₄CNO |
| Alkanes | CβH₂β₊₂; single bonds; methane, butane (LPG) |
| Alkenes | CβH₂β; double bond; ethylene (fruit ripening) |
| Alkynes | CβH₂β₋₂; triple bond; acetylene (welding) |
| Benzene | Aromatic; C₆H₆; solvent (benzol) |
| Chloroform | CHCl₃; stored in dark; oxidises to phosgene |
| TNT | Trinitrotoluene; explosive |
| Coal Types | Anthracite (90% C) > Bituminous > Lignite > Peat |
KEY TAKEAWAYS FOR UPSC
- Urea: First organic compound synthesised (WΓΆhler, 1828)
- Alkanes: Saturated hydrocarbons (CβH₂β₊₂); methane = marsh gas
- Alkenes: Unsaturated (CβH₂β); ethylene ripens fruits
- Alkynes: Unsaturated (CβH₂β₋₂); acetylene used in welding
- Benzene: Aromatic; used as solvent (benzol)
- Chloroform: Stored in dark; forms phosgene in sunlight
- DDT: Chlorinated insecticide; banned in many countries
- Graphene: 2D carbon allotrope; good conductivity
- LPG: Butane + Propane; CNG: Compressed Natural Gas
- Octane number: Higher = better antiknocking property
High-Yield Interactive UPSC Quiz (Chemistry — Organic Chemistry)
Q1. Who synthesised urea first in the laboratory?
Correct Answer: B. Friedrich WΓΆhler synthesised urea in 1828 from ammonium cyanate, disproving vital force theory.
Q2. What is the general formula of alkanes?
Correct Answer: B. Alkanes (saturated hydrocarbons) have the general formula CβH₂β₊₂.
Q3. Which gas is the main constituent of LPG?
Correct Answer: B. LPG (Liquefied Petroleum Gas) mainly consists of butane (C₄H₁₀) and propane.
Q4. Which compound is used for artificial ripening of fruits?
Correct Answer: B. Ethylene (C₂H₄) is used for artificial ripening of green fruits.
Q5. Chloroform on oxidation forms:
Correct Answer: B. Chloroform (CHCl₃) oxidises to phosgene (COCl₂), a poisonous gas, in sunlight.
Q6. The purest form of carbon is:
Correct Answer: B. Diamond is the purest form of carbon.
Q7. What is the octane number of CNG?
Correct Answer: C. CNG (Compressed Natural Gas) has an octane rating of 130.
Q8. Which type of coal has the highest carbon content?
Correct Answer: D. Anthracite has the highest carbon content (~90%) among coal types.
Q9. Which compound is known as "oil of mirbane"?
Correct Answer: B. Nitrobenzene (C₆H₅NO₂) is known as oil of mirbane.
Q10. The Bhopal gas tragedy was caused by leakage of:
Correct Answer: B. The Bhopal gas tragedy (1984) was caused by the leakage of methyl isocyanate (MIC).