Organic Chemistry

Master organic chemistry concepts for RRB exam preparation with comprehensive coverage of carbon compounds, functional groups, and their applications in daily life.

Introduction to Organic Chemistry

What is Organic Chemistry?

Definition

• Organic Chemistry: Study of carbon-containing compounds
• Carbon’s Unique Properties: Forms stable covalent bonds with itself and other elements
• Basis of Life: Foundation of biochemistry and living organisms
• Vast Scope: Millions of known organic compounds

Why Carbon is Special

• Tetravalency: Forms four covalent bonds
• Catenation: Forms chains and rings with other carbon atoms
• Multiple Bonding: Forms single, double, and triple bonds
• Stability: Carbon-carbon bonds are strong and stable

Hydrocarbons

Definition

• Hydrocarbons: Compounds containing only carbon and hydrogen
• Simplest Organic Compounds: Building blocks of organic chemistry
• Energy Sources: Major fuels (petroleum, natural gas)

Saturated Hydrocarbons (Alkanes)

General Properties

Structure

• General Formula: CₙH₂ₙ₊₂
• Single Bonds: Only single C-C and C-H bonds
• Tetrahedral Geometry: 109.5° bond angles
• Saturated: Cannot add more hydrogen

Physical Properties

• Non-polar: Weak intermolecular forces
• Low Boiling Points: Increase with molecular weight
• Insoluble in Water: Soluble in non-polar solvents
• Less Dense than Water: Float on water

Nomenclature

IUPAC Naming

• Identify Longest Chain: Principal carbon chain
• Number Carbons: Start from end giving lowest numbers to substituents
• Name Substituents: Alkyl groups attached to main chain
• Combine Names: Prefix + parent chain + suffix

Common Names

• Methane (CH₄): Natural gas, marsh gas
• Ethane (C₂H₆): Component of natural gas
• Propane (C₃H₈): LPG fuel
• Butane (C₄H₁₀): Lighter fuel, LPG component

Preparation Methods

From Alkyl Halides

• Wurtz Reaction: 2R-X + 2Na → R-R + 2NaX
• Reduction: R-X + H₂ → R-H + HX (with catalyst)

From Alcohols

• Dehydration: R-OH → R=R (with acid catalyst)
• Reduction: R-OH + H₂ → R-H + H₂O

Chemical Properties

Combustion

• Complete Combustion: CₙH₂ₙ₊₂ + (3n+1)/2 O₂ → nCO₂ + (n+1)H₂O
• Incomplete Combustion: Produces CO and C (soot)
• Heat of Combustion: Energy released per mole

Substitution Reactions

• Free Radical Substitution: UV light initiates reaction
• Halogenation: R-H + X₂ → R-X + HX
• Chain Reaction: Initiation, propagation, termination

Unsaturated Hydrocarbons (Alkenes and Alkynes)

Alkenes (C=C)

General Properties

• General Formula: CₙH₂ₙ
• Double Bonds: One or more carbon-carbon double bonds
• Unsaturated: Can add more hydrogen
• Planar Geometry: 120° bond angles around double bond

Physical Properties

• Similar to Alkanes: Non-polar, insoluble in water
• Slightly Higher Boiling Points: Stronger intermolecular forces
• More Reactive: Double bond is reactive site

Common Alkenes

• Ethene (C₂H₄): Ripening agent for fruits
• Propene (C₃H₆): Polymer industry
• Butene (C₄H₈): Synthetic rubber production

Alkynes (C≡C)

General Properties

• General Formula: CₙH₂ₙ₋₂
• Triple Bonds: One or more carbon-carbon triple bonds
• Linear Geometry: 180° bond angles around triple bond
• Most Unsaturated: Can add maximum hydrogen

Physical Properties

• Higher Boiling Points: Stronger intermolecular forces
• More Reactive: Triple bond is very reactive
• Acidic Hydrogen: Terminal alkynes have acidic hydrogen

Common Alkynes

• Ethyne (Acetylene) (C₂H₂): Welding torch fuel
• Propyne (C₃H₄): Organic synthesis
• Butyne (C₄H₆): Chemical intermediate

Addition Reactions

Hydrogenation

• Catalytic Hydrogenation: C=C + H₂ → C-C (with Pt, Pd, Ni)
• Conditions: High pressure, metal catalyst
• Applications: Margarine production, fuel processing

Halogenation

• Addition of Halogens: C=C + X₂ → C-CX₂
• Bromine Test: Disappearing orange color indicates unsaturation
• Vicinal Dihalides: Products have halogens on adjacent carbons

Hydrohalogenation

• Markovnikov’s Rule: H adds to carbon with more H’s
• H-Br, H-Cl, H-I: Common hydrogen halides
• Regioselectivity: Product distribution follows Markovnikov’s rule

Aromatic Hydrocarbons

Benzene and Derivatives

Benzene Structure

• Formula: C₆H₆
• Ring Structure: Hexagonal ring with alternating double bonds
• Resonance: Delocalized π-electrons
• Aromaticity: Special stability due to resonance

Aromatic Properties

• Planarity: All atoms in same plane
• Hückel’s Rule: 4n+2 π-electrons (n=1 for benzene)
• Stability: More stable than expected
• Substitution Reactions: Prefer substitution over addition

Substituted Benzenes

• Toluene (C₆H₅CH₃): Methylbenzene, solvent
• Xylene (C₆H₄(CH₃)₂): Dimethylbenzene, isomers
• Phenol (C₆H₅OH): Hydroxybenzene, antiseptic
• Aniline (C₆H₅NH₂): Aminobenzene, dye intermediate

Electrophilic Aromatic Substitution

Mechanism

• Formation of Electrophile: Strong electrophile generated
• Attack on Benzene: Formation of arenium ion
• Deprotonation: Restoration of aromaticity
• Substitution: One hydrogen replaced

Common Reactions

• Nitration: Introduction of -NO₂ group
• Sulfonation: Introduction of -SO₃H group
• Halogenation: Introduction of halogen atoms
• Alkylation: Introduction of alkyl groups

Functional Groups

Oxygen-containing Functional Groups

Alcohols (-OH)

• Primary Alcohol: -CH₂OH group
• Secondary Alcohol: -CHOH- group
• Tertiary Alcohol: -C(OH) group with three carbons
• Properties: Hydrogen bonding, higher boiling points

Aldehydes (-CHO)

• Structure: Carbonyl group at end of chain
• Oxidation: Can be oxidized to acids
• Reduction: Can be reduced to alcohols
• Examples: Formaldehyde, acetaldehyde

Ketones (>C=O)

• Structure: Carbonyl group within chain
• Stability: Cannot be easily oxidized
• Reduction: Can be reduced to secondary alcohols
• Examples: Acetone, methyl ethyl ketone

Carboxylic Acids (-COOH)

• Acidic Properties: Can donate H⁺ ion
• Hydrogen Bonding: Strong intermolecular forces
• Dimer Formation: Association through hydrogen bonding
• Examples: Acetic acid, formic acid

Esters (-COOR)

• Fruity Odors: Many have pleasant smells
• Formation: Condensation of acid and alcohol
• Hydrolysis: Break down to acid and alcohol
• Examples: Ethyl acetate, methyl benzoate

Nitrogen-containing Functional Groups

Amines (-NH₂, -NHR, -NR₂)

• Basic Properties: Can accept H⁺ ion
• Classification: Primary, secondary, tertiary
• Odor: Often have fishy odor
• Applications: Drugs, dyes, polymers

Amides (-CONH₂)

• Structure: Carbonyl group attached to nitrogen
• Peptide Bonds: Link amino acids in proteins
• Stability: More stable than amines
• Applications: Nylon, pharmaceuticals

Nitriles (-CN)

• Triple Bond: Carbon-nitrogen triple bond
• Hydrolysis: Convert to carboxylic acids
• Polymerization: Form synthetic fibers
• Examples: Acrylonitrile, benzonitrile

Isomerism

Structural Isomerism

Chain Isomerism

• Different Carbon Skeletons: Same formula, different chain arrangement
• Example: Butane (straight chain) vs Isobutane (branched)
• Properties: Different physical and chemical properties

Position Isomerism

• Different Functional Group Position: Same skeleton, different position
• Example: 1-propanol vs 2-propanol
• Properties: Similar but not identical properties

Functional Group Isomerism

• Different Functional Groups: Same formula, different functional groups
• Example: Alcohol vs Ether (C₂H₆O)
• Properties: Significantly different properties

Stereoisomerism

Geometric Isomerism

• Restricted Rotation: Around double bonds or rings
• Cis-Trans: Same side vs opposite side
• Properties: Different physical and chemical properties
• Example: Cis-2-butene vs Trans-2-butene

Optical Isomerism

• Chirality: Non-superimposable mirror images
• Asymmetric Carbon: Carbon with four different groups
• Enantiomers: Pair of optical isomers
• Applications: Pharmaceuticals, flavor compounds

Polymers

Natural Polymers

Carbohydrates

• Cellulose: Plant structural material
• Starch: Energy storage in plants
• Glycogen: Energy storage in animals
• Chitin: Exoskeleton of arthropods

Proteins

• Structure: Polymers of amino acids
• Function: Enzymes, structural components, transport
• Examples: Silk, wool, collagen
• Properties: Biodegradable, biocompatible

Natural Rubber

• Structure: Polymer of isoprene
• Properties: Elastic, waterproof
• Vulcanization: Cross-linking with sulfur
• Applications: Tires, rubber products

Synthetic Polymers

Plastics

• Polyethylene: Plastic bags, containers
• Polypropylene: Automotive parts, textiles
• Polyvinyl Chloride (PVC): Pipes, insulation
• Polystyrene: Packaging, insulation

Synthetic Fibers

• Nylon: Clothing, parachutes, ropes
• Polyester: Clothing, bottles, films
• Acrylic: Sweaters, carpets
• Spandex: Sportswear, elastic materials

Specialty Polymers

• Teflon (PTFE): Non-stick coatings
• Kevlar: Bulletproof vests, tires
• Silicones: Sealants, medical implants
• Polyurethanes: Foams, coatings

Organic Chemistry in Daily Life

Food and Nutrition

Carbohydrates

• Simple Sugars: Glucose, fructose, sucrose
• Complex Carbohydrates: Starch, cellulose
• Sweeteners: Artificial sweeteners, sugar substitutes
• Preservatives: Organic acids, antioxidants

Lipids

• Fats and Oils: Energy storage, insulation
• Fatty Acids: Essential nutrients
• Vitamins: Fat-soluble vitamins A, D, E, K
• Cholesterol: Cell membrane component

Medicines and Drugs

Pain Relievers

• Aspirin: Acetylsalicylic acid, anti-inflammatory
• Paracetamol: Acetaminophen, analgesic
• Ibuprofen: NSAID, pain and fever reducer

Antibiotics

• Penicillin: Beta-lactam antibiotic
• Streptomycin: Aminoglycoside antibiotic
• Tetracycline: Broad-spectrum antibiotic

Vitamins

• Vitamin C: Ascorbic acid, antioxidant
• Vitamin B Complex: Various organic compounds
• Vitamin D: Sterol derivatives

Household Products

Cleaning Agents

• Soaps: Sodium or potassium salts of fatty acids
• Detergents: Synthetic surfactants
• Solvents: Alcohol, acetone, turpentine
• Disinfectants: Phenol, alcohol compounds

Cosmetics

• Fragrances: Essential oils, synthetic aromatics
• Preservatives: Parabens, organic acids
• Emollients: Fatty alcohols, esters
• Colorants: Organic dyes and pigments

Environmental Impact

Pollution

Air Pollution

• Volatile Organic Compounds (VOCs): Evaporate easily
• Particulate Matter: Incomplete combustion products
• Greenhouse Gases: Methane, various VOCs
• Photochemical Smog: Reaction products in atmosphere

Water Pollution

• Pesticides: Organic compounds for pest control
• Herbicides: Weed control chemicals
• Industrial Waste: Solvents, oils, synthetic chemicals
• Pharmaceuticals: Drug residues in water

Sustainability

Green Chemistry

• Renewable Resources: Biomass-based chemicals
• Biodegradable Materials: Environmentally friendly polymers
• Catalysis: Reduce waste and energy consumption
• Atom Economy: Maximize product formation

Alternative Energy

• Biofuels: Ethanol, biodiesel from organic sources
• Solar Cells: Organic photovoltaic materials
• Fuel Cells: Organic proton exchange membranes
• Energy Storage: Organic battery materials

Industrial Applications

Petrochemical Industry

Feedstocks

• Crude Oil: Source of hydrocarbons
• Natural Gas: Methane and higher alkanes
• Coal: Source of aromatic compounds
• Biomass: Renewable organic source

Products

• Fuels: Gasoline, diesel, jet fuel
• Plastics: Various polymeric materials
• Solvents: Industrial and laboratory use
• Chemicals: Intermediates for synthesis

Pharmaceutical Industry

Drug Development

• Active Ingredients: Therapeutic compounds
• Excipients: Inactive ingredients
• Formulations: Drug delivery systems
• Quality Control: Purity and efficacy testing

Manufacturing

• Synthesis: Multi-step organic reactions
• Purification: Crystallization, chromatography
• Analysis: Spectroscopy, chromatography
• Regulation: Safety and efficacy standards

Safety and Handling

Laboratory Safety

Personal Protection

• Gloves: Chemical-resistant materials
• Goggles: Eye protection from splashes
• Lab Coats: Protection from spills
• Fume Hoods: Ventilation for volatile compounds

Storage

• Flammable Materials: Away from heat sources
• Reactive Chemicals: Separate storage
• Toxic Substances: Labeled, secure storage
• Temperature Control: Refrigeration for sensitive compounds

Environmental Safety

Waste Disposal

• Organic Solvents: Special collection and disposal
• Toxic Chemicals: Hazardous waste protocols
• Radioactive Materials: Special procedures
• Biological Materials: Sterilization before disposal

Spill Response

• Containment: Prevent spread of spill
• Neutralization: Chemical treatment if appropriate
• Cleanup: Absorbent materials, proper disposal
• Reporting: Documentation of incident

Practice Questions

Question 1

Write the IUPAC name for CH₃-CH₂-CH₂-CH₃.

Question 2

What is the general formula for alkanes?

Question 3

What type of reaction occurs when ethene reacts with bromine?

Question 4

Name the functional group present in ethanol.

Question 5

What is the difference between aldehydes and ketones?

Question 6

Write the structure of benzene.

Question 7

What is catenation in organic chemistry?

Question 8

Name a natural polymer and its monomer.

Question 9

What is the difference between saturated and unsaturated hydrocarbons?

Question 10

Write the formula for methane.

Quick Reference

Important Functional Groups

Common Reactions

Addition Reactions

• Hydrogenation: Alkene + H₂ → Alkane
• Halogenation: Alkene + X₂ → Dihalide
• Hydrohalogenation: Alkene + HX → Alkyl halide

Substitution Reactions

• Free radical: Alkane + X₂ → Alkyl halide + HX
• Nucleophilic: Alkyl halide + Nu⁻ → Substituted product

Oxidation-Reduction

• Primary alcohol → Aldehyde → Carboxylic acid
• Secondary alcohol → Ketone
• Alkene → Diol (with KMnO₄)

Important Compounds

Industrial Chemicals

• Ethylene: Plastic production
• Propylene: Polypropylene manufacturing
• Benzene: Aromatic compound synthesis
• Toluene: Solvent, fuel additive

Biological Molecules

• Glucose (C₆H₁₂O₆): Energy source
• Ethanol (C₂H₅OH): Alcoholic beverages, fuel
• Acetic Acid (CH₃COOH): Vinegar
• Methane (CH₄): Natural gas

Memory Tips

Naming Conventions

• Meth-: 1 carbon
• Eth-: 2 carbons
• Prop-: 3 carbons
• But-: 4 carbons
• Pent-: 5 carbons

Reaction Patterns

• Alkanes: Substitution reactions
• Alkenes: Addition reactions
• Alkynes: Addition reactions (twice)
• Aromatics: Substitution reactions

Functional Group Priority

1. Carboxylic acid
2. Anhydride
3. Ester
4. Acid halide
5. Aldehyde
6. Ketone
7. Alcohol
8. Amine
9. Alkene/Alkyne
10. Alkane

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