10.1 Fundamentals of organic chemistry

Introduction

  • Organic Chemistry: Field of chemistry which studies carbon-based compounds
  • Homologous Series: A series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit.
    • Hydrocarbons:
      • Alkanes: CnH2n+2
        • Alkyl: CnH2n+1 (Hydrogen of CH4 replaced with other group)
      • Alkenes: CnH2n
      • Alkynes: CnH2n-2
    • Functional Groups
      • Alcohols: CnH2n+1OH
      • Aldehydes: CnH2nO
      • Ketones: CnH2nO
      • Halogenoalkanes: CnH2n+1X
    • Homologous series which contain functional groups also have similar physical and chemical properties within the series. Most of the time its reactive and contains oxygen or nitrogen. In alkene and alkyne, the double and triple bonds are functional groups.

Physical properties of homologous series

  • Generally, as the length of the chain increases, the boiling point increases (due to increased SA, greater chance of intermolecular bonding, more energy to break bonds, higher boiling point)

Chemical formulae of organic compounds

  • Lewis dot structures: Useful to visualize valence electrons
  • Empirical formula: Simplest ratio of atoms in a molecule
  • Molecular formula: Actual number of atoms present in molecule
  • Structural formula: Takes into account the possible structure
    • Full structural formula: 2D representations showing all atoms and bonds and their positions
    • Condensed structural formula: All atoms and relative positions, bonds are omitted
    • Skeletal formula: Carbon and hydrogen atoms are not shown, end of each line and vertex represents C atom. Functional groups shown as well.

Nomenclature (Naming)

  • IUPAC is the world authority in naming and the one used by IB
  • Best way to learn this is to practice naming multiple compounds
  1. Identify the longest chain and thus the root name.
    1. 1 carbon = meth-
    2. 2 carbon = eth-
    3. 3 carbon = prop-
    4. 4 carbon = but-
    5. 5 carbon = pent-
    6. 6 carbon = hex-
    7. 7 carbon = hept-
    8. 8 carbon = oct-
  2. Identify the type of bonding in chain or ring
    1. All single bonds = -an-
    2. One double bond = -en-
    3. One triple bond = -yn-
  3. Identify functional or alkyl groups (this may by at beginning or end of name)
    1. Alkane: only hydrogen joined to chain -e
    2. Hydroxyl: -ol
    3. Amine: amino-
    4. Amide: -amide
    5. Nitrile: -nitrile
    6. Halo: chloro-, bromo- or iodo-
    7. Aldehyde: -al
    8. Ketone: -one
    9. Carboxyl: -oic acid
    10. Ether: -oxy-
    11. Ester: -oate
  4. Use numbers to give position of groups or bonds along chain. Always aim to have lowest numbers.

Structural isomer

  • Compounds with same chemical formula but a different structural formula. Have unique physical and chemical properties

Saturated and unsaturated hydrocarbons

  • Saturated: All carbon to carbon bonds are single bonds (Saturated with H atoms)
  • Unsaturated: Contain double or triple bonds

Functional groups

  • When naming, the position of group is identified by giving the number of the carbon atom to which it is attached
  • When numbering, functional groups take priority over substituents and c-c multiple bonds

Classifying molecules: primary, secondary, and tertiary compounds

  • These are three classes of compounds
    • Primary (1°): Carbon atom bonded to functional group is also bonded to one other carbon atom
    • Secondary (2°): Carbon atom bonded to functional group is also bonded to two other carbon atoms
    • Tertiary (3°): Carbon atom bonded to functional group is also bonded to three other carbon atoms
  • Classifying halogenoalkanes
    • Alkanes undergo free-radical substitution reactions with halogens
    • Whether primary, secondary or tertiary depends on conditions and mechanism of reaction
  • Classifying alcohols
    • Position of the hydroxyl (OH) group determines the class of alcohol
  • Classifying amines
    • Classified depending on number of alkyl groups bonded to the nitrogen atom of functional group
    • N signifies the substituent on the amine. Refer to examples to understand.

Aromatic hydrocarbons

  • Aromatic hydrocarbons are characterized by the presence of benzene
  • Benzene is C6H6 composed of alternating double and single bonds
  • Benzene contains 6 sp2 hybridized carbon atoms bonded to one another, and each carbon bonded to single hydrogen
  • The p orbital overlaps creating a continuous π bond above and below plane of carbon atoms
  • Benzene has a resonance structure

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