For exam revision

Carbon's Role & Structure

• Carbon's Role: Essential backbone for all biological macromolecules (proteins, nucleic acids, carbohydrates, lipids).
• Carbon Atom Structure:
  • Atomic number: 6 (2 inner electrons, 4 valence electrons).
  • Octet Rule: Forms 4 covalent bonds to achieve 8 valence electrons.
  • Tetravalency: Ability to form four stable bonds (C-C, C-H, C-O, C-N, etc.).
  • Geometry: When 4 single bonds, tetrahedral (109.5° bond angles).

Hydrocarbons

• Definition: Organic molecules composed solely of carbon and hydrogen.
• Energy: C-C and C-H bonds store significant potential energy, released upon oxidation.
• Methane (CH4): Simplest hydrocarbon, tetrahedral geometry.

Hydrocarbon Chains

• Can be linear or branched.
• Single Bonds (Alkanes): C-C bonds allow free rotation, leading to conformational flexibility. Each C is sp3 hybridized.
• Double Bonds (Alkenes): C=C bonds restrict rotation, creating rigid, planar regions (sp2 hybridized carbons).
• Triple Bonds (Alkynes): C≡C bonds enforce linear geometry (sp hybridized carbons).
• Nomenclature Prefixes: "eth-" (2 carbons), "prop-" (3 carbons), "but-" (4 carbons).
• Suffixes: "-ane" (single), "-ene" (double), "-yne" (triple).
• Conformation: 3D shape influenced by bond types, crucial for molecular function.

Hydrocarbon Rings

• Aliphatic Hydrocarbons: Contain only single bonds within the ring (e.g., cyclopentane, cyclohexane).
• Aromatic Hydrocarbons: Closed rings with alternating single and double bonds (conjugated system, e.g., benzene). Exhibit resonance stabilization.
• Biological Importance: Aromatic rings in amino acids, steroids (cholesterol, estrogen), DNA bases.