Chapter 13

• Alkenes

  More reactive than alkanes
• Alkenes functional group

  C=C
• Atoms adjacent to the double bond are...

  In a fixed position. The double bond prevents rotation
• Pi bond

  Each carbon bonds with 3 other atoms. The spare p orbitals on the carbons overlap.
• What does the pi bond do?

  Fixes carbon atoms in position and prevents any rotation
• Stereoisomers

  Compounds with the same structural formula but with a different arrangement of the atoms in space.
• Criteria for exhibiting stereoisomerism

  Must contain a double bond, and both carbons must have 2 different group attached to them
• E isomer

  Same groups on opposite sides
• Z isomer

  Same groups on the same side
• What must happen for an isomer to be cis/trans?

  1 of the groups attached to each carbon must be hydrogen. One of the attached groups on each carbon atom of the double bond must be the same (side of the double bond)
• Cis isomer

  Both hydrogens on the same side of the double bond
• Trans isomer

  Both hydrogens are on opposite sides of each isomer
• How do you work out which group has priority?

  Atoms with the highest atomic number are given the highest priority
• If the two first atoms attached to carbon are the same...

  You must find the first point of difference
• How to test for unsaturation?

  Add bromine water and solution will change colour if double bond present
• Alkenes + steam+ acid catalyst (phosphoric)

  Forms an alcohol
• Boiling point of alkenes

  Increases with molecular mass due to increased London forces
• Higher degree of branching

  lower boiling point
• Solubility of alkenes

  Non-polar but soluble in organic solvents
• Electrophilic addition

  Main reaction of alkenes
• Electrophiles

  Electron pair acceptors
• What are electrophiles attracted to?

  Electron rich carbon-carbon double bond
• Electrophilic addition-Step 1

  As molecule nears the alkene, one of the C=C bonds breaks and bonds with the delta positive atom, causing the bond within the molecule to break via heterolytic fission
• Electrophilic Addition-Step 2

  The negative ion bonds with the carbocation
• How do you know which carbon hydrogen has bonded to?


  It bonds to the carbon with the most hydrogens attached
• Primary carbocation

  Attached to one alkyl group
• Secondary carbocation

  Attached to two alkyl groups
• Tertiary carbocation

  Attached to three alkyl groups
• Which of the carbocations is the most stable?

  Tertiary. Primary is least stable
• Hydration Reagent

  Steam
• Hydration pressure and catalyst

  High pressure and phosphoric acid
• Product of direct hydration

  Alcohol
• Hydrogenation reagent

  Hydrogen
• Hydrogenation Catalyst

  Finely divided nickel catalyst
• Product of hydrogenation

  Alkanes
• Monomer

  Small molecule that combines with many other molecules to form a polymer
• Polymer

  A large molecule formed from many thousands of repeat units of smaller molecules known as monomers
• Repeat unit

  Specific arrangement of atoms in a polymer that repeats many times
• Addition polymerisation

  The process in which unsaturated alkene molecules add on to a growing polymer chain one at a time to form a very long saturated molecular chain
• How does branching affect boiling point?

  More branches lowers boiling point as there are less surface points of contact, so the London forces can be more easily broken