ORGANIC CHEMISTRY

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Organic Compounds

Objectives:

1. Derive the names of organic compounds from their general formulas.
2. Relate a compound’s name to its molecular structure.
3. Explain carbon’s tetravalency and its ability to form long chains (catenation).
4. Classify compounds according to their functional groups.
5. Determine empirical and molecular formulas from experimental data.
6. Understand structural isomerism and distinguish between different types.
7. Identify crude oil as a complex mixture of hydrocarbons and relate its fractions to their uses.

Key Concepts and Formulas

Tetravalency of Carbon: Carbon has four valence electrons, enabling it to form four covalent bonds. This property allows carbon to create long chains and complex molecules.

Structural Formula Example: Methane (CH₄) is represented as a central carbon bonded to four hydrogen atoms.

General Formula for Alkanes: Alkanes follow the formula CₙH₂ₙ₊₂, meaning each successive member differs by a CH₂ group.

Example Structure: Butane (C₄H₁₀): CH₃–CH₂–CH₂–CH₃.

IUPAC Nomenclature: Organic compounds are systematically named by identifying the longest carbon chain, numbering substituents, and indicating functional groups.

Example: CH₃CH₂CH₂CH₃ is named n‑butane, while CH₃CH(CH₃)CH₃ is known as isobutane (2‑methylpropane).

Structural Formula Derivation & Naming: Structural (skeletal) formulas show the arrangement of atoms using lines to represent bonds (with carbon atoms at vertices). The compound’s IUPAC name is derived by selecting the longest carbon chain and numbering the substituents.

Explanation: For a straight-chain alkane, the longest chain determines the base name (e.g., n‑butane for a four-carbon chain).

Figure: Diagram showing how structural formulas are constructed and how compound names are derived.

Aliphatic Hydrocarbons & Structural Isomerism

This page discusses alkanes, a major group of aliphatic hydrocarbons, and the concept of structural isomerism. It also includes a list of common alkanes.

Homologous Series: A series of organic compounds where each successive member differs by a CH₂ group and exhibits similar chemical properties.

Example: Methane, Ethane, Propane, Butane, etc.

Substitution Reactions: Alkanes undergo halogenation where a hydrogen atom is replaced by a halogen (e.g., chlorine) under suitable conditions.

General Reaction: CH₄ + Cl₂ → CH₃Cl + HCl

Structural Isomerism: Compounds with the same molecular formula but different arrangements of atoms, typically due to variations in chain branching.

Example: Butane (C₄H₁₀) exists as n‑butane (linear) and isobutane (branched, 2‑methylpropane).

Common Alkanes:

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)
• Pentane (C₅H₁₂)
• Hexane (C₆H₁₄)
• Heptane (C₇H₁₆)
• Octane (C₈H₁₈)
• Nonane (C₉H₂₀)
• Decane (C₁₀H₂₂)

Petroleum and Petrochemicals

This page explains petroleum as a complex mixture of hydrocarbons, its separation through fractional distillation, and related processes like cracking and reforming. It also covers petrochemicals as precursors in organic synthesis.

Composition of Petroleum: Petroleum is a complex blend of various hydrocarbons, along with trace amounts of sulfur, nitrogen, and oxygen compounds.

Key Concept: Fractional distillation separates crude oil into fractions such as gasoline, kerosene, and diesel based on differences in boiling points.

Cracking and Reforming: Cracking breaks large hydrocarbon molecules into smaller ones, while reforming rearranges molecules to enhance fuel quality, notably the octane rating.

Key Concept: Catalytic cracking converts heavy oil fractions into lighter, more valuable products.

Petrochemicals: Chemical products derived from petroleum that serve as building blocks for various organic syntheses.

Key Concept: Petrochemicals such as ethylene and propylene are used to manufacture plastics and synthetic rubbers.

IUPAC Nomenclature and Empirical/Molecular Formula Determination

This section explains the systematic naming of organic compounds and methods for determining their empirical and molecular formulas.

IUPAC Nomenclature: Organic compounds are named by identifying the longest continuous carbon chain, numbering the substituents, and specifying the functional groups. The name reflects the molecule’s structure.

Key Principle: For example, CH₃CH₂CH₂CH₃ is named n‑butane, while CH₃CH(CH₃)CH₃ is known as isobutane (2‑methylpropane).

Empirical and Molecular Formulas: The empirical formula shows the simplest whole-number ratio of elements, while the molecular formula reveals the exact number of atoms in the molecule.

Key Principle: If the empirical formula is CH₂ (mass = 14 g/mol) and the compound’s molar mass is 56 g/mol, the molecular formula is C₄H₈ (56 ÷ 14 = 4).

Additional Concepts in Organic Chemistry & CBT Quiz

This final page covers additional topics such as carbon catenation, functional groups, and structural isomerism, followed by a computer-based test quiz.

Catenation: Carbon’s ability to bond with itself allows the formation of long chains and complex structures.

Key Concept: The formation of ethane (C₂H₆) from two carbon atoms exemplifies catenation.

Functional Groups: Specific groups of atoms within a molecule that determine its chemical behavior and properties (e.g., hydroxyl, carbonyl, carboxyl).

Key Concept: Ethanol (CH₃CH₂OH) is classified as an alcohol because it contains a hydroxyl group.

Structural Isomerism: Compounds with the same molecular formula but different arrangements of atoms.

Key Concept: Butane (C₄H₁₀) exists as both n‑butane (linear) and isobutane (branched).

JAMB CBT Quiz on Organic Compounds

Total time: 900 seconds

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This lesson covers: An introduction to carbon’s tetravalency and catenation The general formulas for aliphatic hydrocarbons (e.g., alkanes: CₙH₂ₙ₊₂) IUPAC nomenclature and empirical/molecular formula determination Structural isomerism and classification by functional groups An overview of petroleum composition, fractional distillation, cracking, and petrochemicals Further topics include: Carbon catenation Functional group properties Structural isomerism