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 CH₂.
• 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., C₂H₆O.
• Empirical formula: Simplest whole number ratio of atoms, e.g., CH₂.
• 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: CₙH₂ₙ₊₂.
• 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: CₙH₂ₙ.
• Pi-bond: Formed by overlapping p-orbitals, restricts rotation.
• Trigonal planar shape: 120° 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.