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Organic Chemistry Study Notes

4.1 Hydrocarbons

  • Definition:

    • A hydrocarbon is defined as a compound made up of hydrogen and carbon only.

4.2 Representing Organic Molecules

  • Types of Formulae:

    • Empirical Formula:

    • This represents the simplest whole number ratio of each element in a compound.

    • Example: For ethene, the empirical formula is CH₂.

    • Molecular Formula:

    • This shows the actual numbers of each element in a compound.

    • Example: For ethene, the molecular formula is C₂H₄.

    • General Formula:

    • A type of empirical formula that represents the composition of any member of an entire class of compounds.

    • Example: For ethene, the general formula is CₙH₂ₙ.

    • Structural Formula:

    • This formula shows the arrangement of atoms within the molecule of a compound.

    • Example: For ethene, the structural formula is CH₂CH₂.

    • Displayed Formula:

    • Shows the symbols for each atom in a compound, with straight lines representing covalent bonds.

    • Example: For ethene, it visually represents the bonding in the structure.

4.3 Key Terms

  • Homologous Series:

    • Defined as a series of compounds that share the same general formula and exhibit similar properties.

  • Functional Group:

    • A functional group is a specific group of atoms within a molecule that is responsible for the chemical reactions of that compound.

  • Isomerism:

    • The phenomenon where compounds share the same molecular formula but exist in different forms due to different arrangements of atoms (known as isomers).

    • Different forms of isomerism exist.

4.4 Naming Compounds Using IUPAC Nomenclature

  • Carbon Prefixes:

    • 1 carbon: Meth-

    • 2 carbons: Eth-

    • 3 carbons: Prop-

    • 4 carbons: But-

    • 5 carbons: Pent-

    • 6 carbons: Hex-

    • Mnemonic: Remember the first four prefixes using “Monkeys Eat Peanut Butter” (MEPB).

  • Functional Group Suffix Rules:

    • Alkanes: -ane (C-C // C-H)

    • Example: Ethane (C₂H₆)

    • Alkenes: -ene (C=C)

    • Example: Ethene (C₂H₄)

    • Alcohols: -ol (OH)

    • Example: Ethanol (C₂H₅OH)

    • Carboxylic Acids: -anoic acid (-COOH)

    • Example: Ethanoic acid (CH₃COOH)

4.5 Writing Structural and Displayed Formulae

  • Instructions:

    • Given the molecular formula, infer the corresponding structural and displayed formulae.

    • Example:

    • Given molecular formula C₂H₆:

      • Structural Formula: CH₃CH₃

      • Displayed Formula: Visual depiction of the bonding between atoms in the molecule.

4.6 Classifying Reactions of Organic Compounds

  • Types of Reactions:

    • Addition Reactions:

    • Characterized by the formation of ONE PRODUCT from TWO REACTANTS.

    • Example: Addition of hydrogen to ethene to yield ethane:

      • Reaction: H₂ + C=C --> H-C-C-H

    • Substitution Reactions:

    • Involves TWO PRODUCTS from TWO REACTANTS.

    • Example: Reaction between hydrogen chloride and ethanol:

      • Reaction: HCl + C₂H₅OH --> C₂H₅Cl + H₂O

    • Combustion Reactions:

    • Involves the reaction of a fuel (hydrocarbon) with OXYGEN.

    • The products are water and carbon dioxide, provided that combustion is COMPLETE.

    • General equation for combustion:

      • Hydrocarbon + O₂ --> CO₂ + H₂O