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Core Organic Chemistry Overview

May 29, 2025

OCR (A) Chemistry A-level

Module 4: Core Organic Chemistry

11.1 Organic Chemistry

  • Hydrocarbons: Compounds containing only carbon and hydrogen.
  • Saturated: Single bonds only.
  • Unsaturated: Contains carbon-carbon multiple bonds.
  • Homologous series: Organic compounds with the same functional group, successive members differ by CHβ‚‚.
  • Simplest homologous series: Alkanes.
  • Functional group: Part of a molecule responsible for its chemical properties.

11.2 Nomenclature of Organic Compounds

  • Aliphatic: Carbon atoms in unbranched/branched chains or non-aromatic rings.
  • Acyclic: Non-aromatic ring, with/without branches.
  • Aromatic: Carbon atoms in a benzene ring.
  • Alkyne: Contains at least one triple carbon-carbon bond.
  • Prefix cyclo-: For alicyclic compounds.

11.3 Representing Formulae

  • Molecular formula: Shows number and type of atoms, e.g., Cβ‚‚H₆O.
  • Empirical formula: Simplest whole number ratio of atoms, e.g., CHβ‚‚.
  • General formula: Simplest algebraic formula for a homologous series.
  • Displayed formula: Shows positioning of all atoms and bonds.
  • Structural formula: Minimal detail showing atom arrangement.

11.4 Isomerism

  • Structural isomers: Same molecular formula, different structural formula.
  • Perfume isomers: Linalool (lavender), Geraniol (rose).

11.5 Reaction Mechanisms

  • Homolytic fission: Bonded atoms take one shared electron each, forming radicals.
  • Heterolytic fission: One atom takes both electrons, forming ions.
  • Curly arrows: Show electron pair movement.
  • Types of reactions:
    • Addition: Two reactants form one product.
    • Substitution: Replacement of atoms/groups.
    • Elimination: Removal of small molecule from larger molecule.

12.1 Properties of Alkanes

  • General formula: Cβ‚™Hβ‚‚β‚™β‚Šβ‚‚.
  • Sigma bonds: Overlapping orbitals, allow free rotation.
  • Fractional distillation: Separates crude oil.
  • Boiling point trends: Longer chains and fewer branches increase boiling points.

12.2 Chemical Reactions of Alkanes

  • Alkanes are less reactive due to strong C-C/C-H bonds and non-polar nature.
  • Used as fuels: readily available, burn cleanly.
  • Carbon monoxide: Highly toxic, prevents oxygen transport in the body.

13.1 Properties of Alkenes

  • General formula: Cβ‚™Hβ‚‚β‚™.
  • Pi-bond: Formed by overlapping p-orbitals, restricts rotation.
  • Trigonal planar shape: 120Β° around double bond.

13.2 Stereoisomerism

  • Stereoisomers: Same structural formula, different spatial arrangement.
  • Cis-trans isomerism: A type of E/Z isomerism.
  • Cahn-Ingold-Prelog rules: Determine priority for E/Z naming.

13.3 Reactivity of Alkenes

  • More reactive than alkanes due to weaker pi-bond which is more exposed.

13.4 Electrophilic Addition

  • Electrophile: Electron pair acceptor.
  • Mechanisms involve breaking of double bonds and forming new bonds with electrophiles.
  • Markovnikov's rule: Predicts major product formation.

13.5 Polymerisation

  • Polymerisation: Formation of polymers from monomers, e.g., poly(ethene).
  • Disposal and recycling: Non-biodegradable challenge, recycling processes, and development of biodegradable polymers.

14.1 Properties of Alcohols

  • Compared to alkanes, alcohols have higher melting points and greater solubility due to hydrogen bonding.
  • Classification: Primary, secondary, and tertiary.

14.2 Reactions of Alcohols

  • Increase in carbon chain length increases heat produced per mole when burnt.

15.1 Chemistry of the Haloalkanes

  • Nucleophile: Electron pair donor attracted to positive carbon in haloalkanes.
  • Hydrolysis Mechanism: Involves substitution of halogen by hydroxide ion.
  • Rate of Hydrolysis: Dependent on carbon-halogen bond strength.

15.2 Organohalogen Compounds and Environment

  • Ozone layer: Protects from UV radiation, CFCs contribute to ozone depletion.
  • Alternatives and regulations: Development of non-toxic alternatives and environmental concerns.

16.1 Practical Techniques in Organic Chemistry

  • Quick-fit apparatus: Used for heating, reflux, and distillation.
  • Drying agents: Used to purify organic products.

17.1 Mass Spectrometry

  • Mass-to-charge ratio detection: Identifies molecular structure.
  • Fragmentation: Provides compound identification.

17.2 Infrared Spectroscopy

  • IR absorption: Related to bond vibrations, used to identify organic molecules.
  • Applications: Pollution monitoring and breath analysis.