Hydrocarbons and Their Compounds

1. Introduction

Compounds are substances made of two or more elements chemically combined.

Compounds are classified into:

Inorganic (non-carbonic) compounds – obtained from minerals (e.g., salts, oxides).

Organic (carbonic) compounds – obtained from plants and animals.

Note: All compounds of carbon except CO, CO₂, carbonates, bicarbonates, and carbides are organic compounds.

Hydrocarbons are carbonic compounds that contain only carbon (C) and hydrogen (H).

Examples of hydrocarbons: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

Sources of hydrocarbons: Petroleum, natural gas, coal, and plant/animal sources.

2. Organic Compounds

Organic compounds consist mainly of carbon, hydrogen, and sometimes oxygen, nitrogen, halogens, sulfur, or phosphorus.

They are covalently bonded compounds.

Examples: Methane, Ethane, Ethene, Acetylene, Methanol, Proteins, Oils.

Branch of chemistry that studies these compounds: Organic Chemistry or Carbon Chemistry.

Combustibility:

Combustible substances (e.g., wood, kerosene) → Organic

Non-combustible substances (e.g., glass, stone) → Inorganic

3. Hydrocarbons

Composed only of carbon and hydrogen.

Main source: Petroleum.

Types based on carbon-carbon bonds:

Saturated hydrocarbons (Alkanes) – single bonds only

Unsaturated hydrocarbons – double or triple bonds

3.1 Saturated Hydrocarbons (Alkanes)

Definition: Hydrocarbons with only single bonds between carbon atoms.

Properties: Stable, less reactive, called paraffins.

General formula: CₙH₂ₙ₊₂

Examples:

NameMolecular FormulaStructural FormulaMethaneCH₄H–C–HEthaneC₂H₆H–C–C–HPropaneC₃H₈H–C–C–C–HButaneC₄H₁₀H–C–C–C–C–H

C–C–C–C–H

3.2 Unsaturated Hydrocarbons

Definition: Hydrocarbons with double or triple bonds between carbon atoms.

Properties: Less stable, highly reactive, called olefins.

(a) Alkene

Hydrocarbons with double bonds

General formula: CₙH₂ₙ

Examples:

NameMolecular FormulaStructural FormulaEtheneC₂H₄H₂C=CH₂PropeneC₃H₆CH₃–CH=CH₂ButeneC₄H₈CH₃–CH₂–CH=CH₂

(b) Alkyne

Hydrocarbons with triple bonds

General formula: CₙH₂ₙ₋₂

Examples:

NameMolecular FormulaStructural FormulaEthyneC₂H₂HC≡CHPropyneC₃H₄CH₃–C≡CHButyneC₄H₆CH₃–C≡C–CH₃

4. Differences between Saturated and Unsaturated Hydrocarbons

FeatureSaturated (Alkanes)Unsaturated (Alkene/Alkyne)Bond typeSingle bondsDouble or triple bondsStabilityStableLess stable, reactiveGeneral nameAlkaneAlkene (double), Alkyne (triple)General formulaCₙH₂ₙ₊₂Alkene: CₙH₂ₙ, Alkyne: CₙH₂ₙ₋₂

5. Homologous Series

Definition: Series of hydrocarbons with similar structure, chemical properties, and the same general formula.

Each member differs by CH₂ unit from the next.

Example: Methane → Ethane → Propane → Butane

Molecular weight difference between successive members: 14

6. Alkyl Radical

Definition: A group formed by removing one hydrogen from an alkane molecule.

General formula: CₙH₂ₙ₊₁

Example: –CH₃, –C₂H₅

7. Functional Groups

Definition: Atom or group of atoms that determines the chemical reactivity of an organic compound.

Examples:

Hydroxyl group: –OH (alcohols)

Carbonyl group: –CHO (aldehydes)

Carboxyl group: –COOH (acids)

8. Nomenclature of Hydrocarbons (IUPAC System)

Step 1: Find the root based on number of carbon atoms:

C atomsRoot1Meth2Eth3Prop4But5Pent6Hex7Hept8Oct9Non10Dec

Step 2: Add suffix based on bond type:

Single → -ane, Double → -ene, Triple → -yne

Example: C₂H₆ → Ethane (2 carbons, single bond)

9. Important Hydrocarbons and Their Uses

Methane (CH₄)

Source: Marshy areas, biogas, sewage gas

Properties: Colorless, odorless, tasteless, insoluble in water

Uses:

Cooking fuel (biogas)

Making carbon black for ink, paint, polish

Preparation of chloroform, carbon tetrachloride, methanol

Ethane (C₂H₆)

Found in natural gas, petroleum

Uses:

Heat source in welding

Making ethyl chloride, nitroethane

Propane (C₃H₈)

Found in natural gas

Uses: Fuel, coolant, raw material for carbon compounds

Butane (C₄H₁₀)

Found in petroleum

Uses: LPG fuel, synthetic rubber

10. Alcohols

Compounds derived from alkanes by replacing H with –OH group

General formula: CₙH₂ₙ₊₁OH

Functional group: Hydroxyl (–OH)

Types:

Monohydric (1 –OH) → Methanol, Ethanol

Dihydric (2 –OH) → Glycol (e.g., Ethane-1,2-diol)

Trihydric (3 –OH) → Glycerol

Uses

Methanol: Solvent, formaldehyde, fuels

Ethanol: Drinks, antiseptics, lab preservative, manufacturing

Glycol: Coolants, antifreeze

Glycerol: Soap, cosmetics, sweetening, skin protection

11. Hydrogenation

Process of converting unsaturated fatty acids to saturated fatty acids by adding hydrogen (H₂).

Example: Vegetable oil → Vanaspati ghee

12. Summary

Hydrocarbons: Only C and H, found in petroleum, natural gas

Saturated: Single bond, stable, alkanes

Unsaturated: Double/triple bonds, reactive, alkenes/alkynes

Organic compounds: Contain C, covalently bonded, derived from plants/animals

Functional groups define reactivity and type of organic compound

IUPAC nomenclature gives systematic names