Unit 4 and 6: terms to remember (fixed)

• Hydrocarbon

  A compound containing carbon and hydrogen only.
• Saturated

  Contain single bonds only, arranged in straight or branched chains and non-aromatic rings.
• Unsaturated

  Contain multiple carbon-carbon bonds, including C=C, C≡𝐶 and aromatic rings.
• Homologous series

  A family of compounds with the same functional group but with each successive member differing by a CH2 group.
• Functional group

  An atom or a group of atoms responsible for chemical properties of a compound.
• Aliphatic

  A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings.
• Alicyclic

  An aliphatic compound arranged in non-aromatic rings with or without side chains.
• Aromatic

  A compound containing a benzene ring.
• Alkyl group

  A group derived from an alkane by removing 1 H atom. The name has the suffix -yl instead of -ane.
• General formula of alkanes

  CnH2n+2.
• General formula of alkenes

  CnH2n.
• General formula of alcohols

  CnH2n+1OH.
• General formula of carboxylic acids

  CnH2nO2.
• General formula of ketones

  CnH2nO.
• Structural isomers

  Compounds with the same molecular formula but different structural formula.
• Types of bond fission

  Homolytic fission - breaking of a covalent bond when each of the bonded atoms takes one of the shared electrons from the bond. Heterolytic fission - breaking of a covalent bond when one of the bonded atoms takes both of the shared electrons from the bond.
• Curly arrows show...

  The movement of an electron pair when a bond is being made or broken.
• Examples of substitution reactions

  Alkanes to haloalkanes, Haloalkanes to amines, Benzene to nitrobenzene, chlorobenzene.
• Examples of addition reactions

  Alkenes to alkanes, alcohols, haloalkanes, dihaloalkanes, Carbonyls to alcohols and to hydroxynitriles.
• Examples of elimination reactions: Dehydration of alcohols
• Examples of condensation reactions

  Esterification, Acyl chlorides and amines to amides.
• Sigma bond

  Forms when two orbitals overlap head-on.
• Shapes in alkanes and bond angles

  Each carbon has a tetrahedral shape as it has 4 bonding pairs and no lone pair. The bond angle is 109.5.
• Trend in boiling points for straight chain alkanes

  The boiling point increases as the chain length increases.
• Comparing isomers with straight and branched chains

  The boiling point of branched isomers is lower than straight chain

  isomers.

  • fewer surface points of contact between branched molecules

  • weaker London forces between molecules

  • less energy needed to overcome the forces
• Reactions of alkanes, products and conditions, mechanism

  + Cl2 or Br2 ➔ haloalkanes, UV present, Mechanism: free radical substitution.
• Limitations of radical substitution

  Further substitution: more than 1 H can be substituted, forming a mixture of haloalkanes. Substitution on a different carbon atom: a mixture of isomers produced.

  Problem: difficult To separate the products
• How is the double made

  There is one sigma bond and 1 pi bond. A pi bond is formed by a sideways overlap of p orbitals.
• Compare the pi and sigma bonds

  Sigma bonds can be formed by 2 s, 2p, or an s and a pi orbital overlapping while pi is made by 2 pi orbitals overlapping. Sigma bonds form between the two bonding atoms and pi bonds form above and below the bonding atoms.
• Shape and bond angles around a C atom in C=C

  3 regions of electron density around the C atom. They repel as far as possible. Bond angle 120°.
• Stereoisomers

  Compounds with the same structural formula but a different arrangement of atoms in space.
• Reasons E/Z

  Rotation around the double bond is restricted and the groups attached to each carbon are fixed relative to each other.
• What is cis-trans?

  Special case of E/Z. C=C bond. Different groups attached to each carbon atom of the C=C, and one of the groups on each C=C must be hydrogen.
• Using the CIP rules

  Based on the atomic number of the atom bonded to each C in C=C. The atom with a higher atomic number is given a higher priority. Groups with higher priority on the same side of C=C (below or above) ➔ Z isomer. Groups with higher priority placed diagonally across the C=C ➔ E isomer.
• Four reactions of alkenes, products and conditions

  + steam or H2O(g) / H3PO4 ➔ alcohols,

  + H2(g) / Ni ➔ alkanes,

  + halogens ➔ dihaloalkanes,

  + hydrogen halides ➔ haloalkanes.
• How to test for C=C?

  Add bromine water. It decolourises (changes from brown to colourless).
• Definition of an electrophile


  An atom or a group of atoms that is attracted to an electron-rich centre and accepts an electron pair.
• Curly arrows start from ...

  A bond, A lone pair, A negative charge.
• What is a carbocation?

  A species with a positively charged carbon atom.
• Markovnikoff's rule

  When a hydrogen halide reacts with an unsymmetrical alkene, the hydrogen attaches itself to the carbon atom with the greater number of hydrogens.