Introduction to Organic Chemistry (AQA Revision Video)

Lecturer

• Chris Harrison from Mallory Cheaters.com

Overview

• This video serves as a revision guide for AQA's organic chemistry topics, intended to prepare you for exams.
• The PowerPoint presentation used can be purchased via a link in the video description.

Types of Formulas

General Formula

• An algebraic formula applicable to chemicals in a family (e.g., alkanes, alkenes, alcohols).
  • Alkanes: CnH2n+2
  • Alkenes: CnH2n
  • Alcohols: CnH2n+1OH
• Importance: Knowing these is critical for exam questions.

Molecular Formula

• Represents the actual number of atoms in a molecule. Example: C2H6 (ethane).

Empirical Formula

• Simplest whole number ratio of atoms in a compound. Example: CH3 for C2H6.

Structural Formula

• Arrangement of atoms in a molecule without showing bonds. Example: butan-1-ol as CH3CH2CH2CH2OH.

Skeletal Formula

• Shows bonds of the carbon skeleton; hydrogen and carbon atoms are not shown but functional groups are. Example: zigzag lines representing carbons.

Displayed Formula

• Shows the arrangement of all atoms and bonds in a molecule. Example: 2-chloropropane displayed with all bonds.

Homologous Series

• Compounds with the same functional group and general formula.
• Example: Alkenes (CnH2n)
• Successive members increase by CH2.
  • Methanol, Ethanol, Propanol, Butanol, etc.
• Types include:
  • Alkanes (suffix: -ane) Example: Butane
  • Alkenes (suffix: -ene) Example: Propene
  • Alcohols (suffix: -ol) Example: Ethanol
  • Aldehydes (suffix: -al) Example: Propanal
  • Ketones (suffix: -one) Example: Propanone
  • Carboxylic Acids (suffix: -oic acid) Example: Butanoic acid
  • Haloalkanes: Include prefixes like fluoro, chloro, bromo, iodo
  • Cycloalkanes: Prefix cyclo- and suffix -ane

Nomenclature

• Based on IUPAC rules (International Union of Pure and Applied Chemistry)
• Steps:
  1. Find the longest continuous chain of carbon atoms (the stem).
  2. Identify the principal functional group (suffix).
  3. Number the carbon chain such that the principal functional group gets the lowest number possible.
  4. Write the prefixes for any side chains or less important functional groups in alphabetical order.
  5. Use multipliers (di-, tri-, tetra-) for multiple identical groups.
• Example: 3-methylbutan-1,1-diol for a molecule with a methyl group on C3 and two OH groups on C1.

Mechanisms

• Chemical mechanisms show electron movement.
• Curly arrows: Show movement of a pair of electrons.
• Example reaction: OH- with bromoethane.

Isomerism

Structural Isomers

• Same molecular formula but different structural formulas.
• Types:
  • Chain Isomers: Different arrangement of carbon skeleton. Example: Pentane and 2-methylbutane.
  • Positional Isomers: Different position of the functional group on the carbon skeleton. Example: Pentan-1-ol and Pentan-2-ol.
  • Functional Group Isomers: Different functional groups but same molecular formula. Example: Pent-2-ene and Cyclopentane.

Stereoisomers (E-Z Isomerism)

• Same structural formula but different spatial arrangement of atoms.
• E-Z (cis-trans) Isomerism:
  • Requires restricted rotation around double bond and two different groups attached to each carbon of the double bond.
  • E (entgegen): Opposite sides.
  • Z (zusammen): Together on the same side.
• Cahn-Ingold-Prelog Rules: Used to prioritize groups when more than two different groups are attached to a double bond.
  • Atomic number determines priority.
• Example: E-2-bromo-2-butene versus Z-2-bromo-2-butene.

Summary

• Introduction covers basic organic chemistry concepts necessary for AQA exams.
• Ensure understanding of formula types, homologous series, nomenclature, mechanisms, and isomerism.
• PowerPoints are available for purchase if needed for further study.