Module 4 Core Organic Chemistry

• Hydrocarbons


  Compound containing carbon and hydrogen only
• Saturated


  • Has single bonds only
• Unsaturated


  • Contains carbon-carbon multiple bonds
• Homologous series


  A series of organic compounds having the same functional group but with each successive member differing by a CH2
• Functional group


  Part of molecule largely responsible for molecule's chemical properties
• Aliphatic


  Carbon atoms joined in unbranched/branched chains, or non-aromatic rings
• Acyclic


  An aliphatic compound arranged in non-aromatic ring, with/without branches
• Aromatic


  Some/all carbon atoms found in a benzene ring
• Alkyne


  Contains at least one triple carbon-carbon bond
• Prefix cyclo-


  For alicyclic
• Molecular formula


  Shows number of + type of atoms of each element in a molecule e.g. C2H6O
• Empirical formula


  Simplest whole number ratio of atoms of each element present in a compound e.g. C4H8 → CH2
• General formula


  Simplest algebraic formula for any member of a homologous series
• Displayed formula


  Shows relative positioning of all the atoms in a molecule and the bonds between them
• Structural formula


  Uses the smallest amount of detail necessary to show the arrangement of atoms in a molecule
• Structural isomers


  Compounds with same molecular formula but different structural formula, can have same functional group at different point/different functional group
• Homolytic fission


  Each of the covalently bonded atoms takes one of the shared electrons, forms 2 radicals
• Heterolytic fission


  One of covalently bonded atoms takes both the electrons, one becomes -ve ion and one becomes +ve ion
• Curly arrows


  Show movement of a pair of electrons
• Addition


  Two reactants join to make one product
• Substitution


  Atom or group of atoms is replaced by a different atom/group of atoms
• Elimination


  Removal of a small molecule from a larger molecule
• Alkanes


  General formula: CnH2n+2
• Alkanes


  • Each carbon is joined to 4 other atoms by single covalent sigma bonds
  • Sigma bond: the result of overlapping of 2 orbitals, one from each bonding atom, positioned on line directly between bonding atoms
  • 3d tetrahedral arrangement around each carbon, 109.5°
  • Sigma bonds act as axes around which atoms can rotate freely, so not rigid shape (can change)
• Fractional distillation is used to separate crude oil into fractions
• Increased chain length


  Greater surface area contact, stronger London forces, higher boiling point
• More branching


  Less surface area contact, weaker London forces, lower boiling point
• Alkanes


  • Not very reactive: C-C/C-H bonds strong, C-C bonds non-polar, C-H bonds can be considered non polar (C and H have similar electronegativities)
• Alkanes as fuels


  Readily available, easy to transport, burn to release no toxic products
• Carbon monoxide is colourless, odourless and highly toxic. Combines irreversibly with haemoglobin in red blood cells to form carboxyhaemoglobin preventing oxygen passing round body. Can turn lips bright pink
• Alkenes


  General formula CnH2n
• Alkenes


  • Carbons in double bond have formed three sigma bonds, meaning they have one electron left in a p-orbital, which forms a pi-bond by sideways overlap of 2 p-orbitals. Pi-electron density concentrated above + below line joining nuclei bonded atoms
  • Pi-bond locks carbon atoms in position, can't rotate
  • Trigonal planar shape around double bond, 120°
• Stereoisomers


  Have same structural formula but a different arrangement atoms in space
• Cis-trans isomerism


  Arises because rotation around double bond is restricted + groups attached to each carbon are fixed relative to each other
• E/Z isomerism


  A compound must have: C=C bond & different groups attached to each carbon
• Cis-trans


  A type of E/Z isomerism where one of groups on each carbon must be a hydrogen
• Cahn-ingold-Prelog rules


  Groups of higher priority same side double bond=Z, groups of higher priority diagonally placed=E. highest priority determined by Mr of atoms attached directly to carbons in double bond (if atom is same, go along chain until 1st different)
• Alkenes


  • More reactive than alkanes: pi bond enthalpy is less so bond is weaker & bond is more exposed as on top/bottom so broken more readily
• Electrophilic addition in alkenes


  • Double bond in alkene is an area of high electron density due to pi-electrons. High electron density attracts electrophiles
  • Electrophile: an electron pair acceptor (usually a +ve ion or a molecule with atom with δ+ charge)
• Mechanism of electrophilic addition of alkene + hydrogen bromide

  1. Hydrogen bromide is polar and has dipoles because bromine is more electronegative

  2. Electron pair in π-bond attracted to δ+ hydrogen, double bond breaks

  3. Bond forms between H and carbon atom from double bond

  4. H-Br bond breaks by heterolytic fission, electron pair goes to Br

  5. Br- and carbocation formed, they react to form product