HYDROCARBONS AND BASIC TERMINOLOGIES IN ORGANIC CHEMISTRY
Introduction
Organic chemistry is the branch of chemistry that deals with carbon-containing compounds, particularly those containing carbon-hydrogen (C-H) bonds. The vast majority of organic compounds are derived from hydrocarbons, making them the foundation of organic chemistry.
Hydrocarbons are important sources of fuel, raw materials for industries, and building blocks for numerous synthetic products such as plastics, pharmaceuticals, detergents, dyes, and fertilizers.
Basic Terminologies in Organic Chemistry
Before studying hydrocarbons, it is important to understand some common terms used in organic chemistry.
1. Organic Compounds
Organic compounds are compounds that contain carbon atoms bonded to hydrogen atoms and may also contain oxygen, nitrogen, sulfur, phosphorus, or halogens.
Examples:
i. Methane (CH₄)
ii. Ethanol (C₂H₅OH)
iii. Acetic acid (CH₃COOH)
2. Hydrocarbons
Hydrocarbons are organic compounds made up of only two elements, carbon and hydrogen.
Examples:
i. Methane (CH₄)
ii. Ethane (C₂H₆)
iii. Benzene (C₆H₆)
Hydrocarbons are classified into:
Aliphatic hydrocarbons
Aromatic hydrocarbons
3. Homologous Series
A homologous series is a family of organic compounds having the same functional group and general formula, with successive members differing by a CH₂ group
Examples:
Compound | Molecular Formula |
Methane | CH₄ |
Ethane | C₂H₆ |
Propane | C₃H₈ |
Butane | C₄H₁₀ |
Characteristics:
i. Similar chemical properties
ii. Gradual change in physical properties
iii. Same functional group
iv. Successive members differs by a CH₂
4. Functional Group
A functional group is an atom or group of atoms responsible for the characteristic chemical reactions of an organic compound.
Examples:
Functional Group | Name |
–OH | Alcohol |
–COOH | Carboxylic Acid |
–CHO | Aldehyde |
–NH₂ | Amine |
5. Isomerism
Isomerism is the phenomenon where compounds have the same molecular formula but different structural arrangements.
Example:
C₄H₁₀ exists as:
i. n-Butane
ii. Isobutane
6. Saturated and Unsaturated Compounds
Saturated Compounds
Contain only single carbon-carbon bonds.
Example:
i.Ethane (C₂H₆)
Unsaturated Compounds
Contain at least one double or triple bond.
Examples:
i. Ethene (C₂H₄)
ii. Ethyne (C₂H₂)
7. Molecular Formula
Shows the actual number of atoms present in a molecule.
Example:
i. Ethane = C₂H₆
8. Structural Formula
Shows how atoms are connected within a molecule.
Example:
CH₃–CH₃
Hydrocarbons
Hydrocarbons are the simplest organic compounds and form the basis of all organic chemistry.
Sources of Hydrocarbons
Crude oil (Petroleum)
Natural gas
Coal
Biomass
Classification of Hydrocarbons
Hydrocarbons are broadly classified into:
1. Aliphatic Hydrocarbons
These consist of straight-chain, branched-chain, or non-aromatic cyclic compounds.
They are divided into:
A. Alkanes
Alkanes are saturated hydrocarbons containing only single covalent bonds.
General Formula
CₙH₂ₙ₊₂
Examples
Alkane | Formula |
Methane | CH₄ |
Ethane | C₂H₆ |
Propane | C₃H₈ |
Butane | C₄H₁₀ |
Properties
Relatively unreactive
Undergo combustion
Undergo substitution reactions
Uses
Domestic cooking gas
Fuel for vehicles
Industrial heating
B. Alkenes
Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond.
General Formula
CₙH₂ₙ
Examples
Alkene | Formula |
Ethene | C₂H₄ |
Propene | C₃H₆ |
Butene | C₄H₈ |
Properties
More reactive than alkanes
Undergo addition reactions
Uses
Manufacture of plastics
Production of alcohols
Chemical synthesis
C. Alkynes
Alkynes are unsaturated hydrocarbons containing at least one carbon-carbon triple bond.
General Formula
CₙH₂ₙ₋₂
Examples
Alkyne | Formula |
Ethyne | C₂H₂ |
Propyne | C₃H₄ |
Properties
Highly reactive
Undergo addition reactions
Uses
Welding and cutting metals
Production of industrial chemicals
Aromatic Hydrocarbons
Aromatic hydrocarbons contain one or more benzene rings.
Examples
Benzene (C₆H₆)
Toluene (C₇H₈)
Naphthalene (C₁₀H₈)
Characteristics
Highly stable
Possess delocalized electrons
Undergo substitution reactions
Uses
Solvents
Dye manufacture
Pharmaceutical production
Reactions of Hydrocarbons
1. Combustion
Hydrocarbons burn in oxygen to produce carbon dioxide and water.
Example:
CH₄ + 2O₂ → CO₂ + 2H₂O
Uses:
i. Energy generation
ii. Domestic cooking
iii. Transportation
2. Substitution Reaction
Common in alkanes and aromatic compounds.
Example:
CH₄ + Cl₂ → CH₃Cl + HCl
3. Addition Reaction
Occurs in alkenes and alkynes.
Example:
C₂H₄ + H₂ → C₂H₆
4. Polymerization
Small molecules combine to form large molecules called polymers.
Example:
n(C₂H₄) → (–CH₂–CH₂–)ₙ
Polymer produced: Polyethene
Importance of Hydrocarbons
Source of energy and fuel.
Raw materials for petrochemical industries.
Manufacture of plastics and synthetic fibres.
Production of detergents and solvents.
Pharmaceutical manufacturing.
Production of fertilizers and pesticides.
Environmental Effects of Hydrocarbon Use
Advantages
i. High energy content
ii. Easily available
iii. Versatile industrial applications
Disadvantages
i. Air pollution
ii. Greenhouse gas emissions
iii. Global warming
iv. Oil spill contamination
Conclusion
Hydrocarbons are the fundamental compounds of organic chemistry and serve as the building blocks for countless organic substances. Understanding their classification, properties, reactions, and applications provides a strong foundation for studying advanced organic chemistry. Knowledge of key organic chemistry terminologies such as functional groups, homologous series, isomerism, and saturation is essential for understanding the behavior and reactions of organic compounds.
Objectives QuestionsInstructions: Choose the correct option (A–D) for each question.