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, which enables it to form four covalent bonds. This unique property allows carbon to create long chains and complex molecules.

Structural Formula Example: Methane (CH₄) is represented as a central carbon atom 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) is represented as: CH₃–CH₂–CH₂–CH₃.

IUPAC Nomenclature: Organic compounds are systematically named by identifying the longest carbon chain and noting the positions of substituents and functional groups.

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

Structural Formula Derivation & Naming: The structural formula (or skeletal formula) is a representation that shows how atoms are bonded together using lines for bonds. In skeletal formulas, carbon atoms are assumed at the vertices and intersections, while hydrogen atoms bonded to carbon are omitted for simplicity. The IUPAC name is derived by identifying the longest continuous carbon chain, numbering it, and naming any substituents.

Figure Explanation: The diagram below illustrates the derivation of a skeletal formula and how the compound’s name is determined.

Figures: The first diagram illustrates the skeletal formula derivation; the second shows how the compound’s name is derived from its structure.

Aliphatic Hydrocarbons & Structural Isomerism

This page covers alkanes—a class of aliphatic hydrocarbons—and explains structural isomerism. It also includes a list of common alkanes.

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

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

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

General Reaction: CH₄ + Cl₂ → CH₃Cl + HCl

Structural Isomerism: Organic compounds with the same molecular formula but different arrangements of atoms. In alkanes, this usually means differences in branching.

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

List of 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 such as cracking and reforming. It also covers petrochemicals used as feedstocks in organic synthesis.

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

Key Concept: Fractional distillation separates crude oil into fractions (e.g., gasoline, kerosene, diesel) based on boiling point differences.

Cracking and Reforming: Cracking breaks down heavy hydrocarbons into lighter ones, while reforming rearranges molecular structures to improve fuel quality and increase the octane rating.

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

Petrochemicals: Chemical products derived from petroleum that are used as starting materials for a wide range of organic syntheses.

Key Concept: Petrochemicals such as ethylene and propylene are essential for producing 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 substituents, and indicating functional groups. This systematic method reflects the molecular structure of the compound.

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

Empirical and Molecular Formulas: The empirical formula is the simplest whole-number ratio of elements, whereas the molecular formula indicates the actual number of atoms in a molecule.

Key Principle: For a compound with an empirical formula CH₂ (14 g/mol) and a molar mass of 56 g/mol, the molecular formula is C₄H₈.

Additional Concepts and CBT Quiz

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

Catenation: Carbon’s ability to form strong covalent bonds with itself, enabling the formation of long chains and complex molecular structures.

Key Concept: The formation of ethane (C₂H₆) illustrates carbon catenation.

Functional Groups: Specific groups of atoms within molecules that determine the compound’s chemical reactivity and properties (e.g., hydroxyl, carbonyl, carboxyl groups).

Key Concept: Ethanol (CH₃CH₂OH) is classified as an alcohol because of its hydroxyl (-OH) group.

Structural Isomerism: Compounds with the same molecular formula but different arrangements of atoms, leading to differences in physical and chemical properties.

Key Concept: Butane (C₄H₁₀) exists in two forms: 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