C14 alkenes

• alkenes are unsaturated hydrocarbons
• alkenes contain a C=C bond, a carbon-carbon double bond
• the general formula for alkenes is C(n)H(2n)
• a C=C bond is an area of high electron density, so it is attacked by electrophiles
• electrophiles are positively charged molecules which want to accept an electron pair
• alkenes are unsaturated so tend to undergo addition reactions
• the reactions of alkenes are almost always electrophilic addition
• there can be no rotation around a C=C bond because of the overlapping p-orbitals, this allows different isomers to be formed
• the two types of isomer that alkenes can form are position isomers and geometrical isomers
• position isomers are alkenes with the double bond in different positions
• geometrical isomers are alkenes with the same structural formula but a different arrangement of atoms in space
• cahn-ingold-prelog rules state that around a C=C bond, the substituent with the highest atomic mass will receive highest priority
• using CIP rules, hydrogen atoms will always have the lowest priority as they have the lowest atomic mass
• CIP rules mean that the species which define whether an alkene is the E isomer or the Z isomer are the heaviest one on each side
• the only forces which act between alkenes are van der Waals forces, so they have similar melting and boiling points to alkanes, and melting and boiling points increase with the number of carbon atoms present
• alkenes are not soluble in water
• mechanism of electrophilic addition:

  • electrophile is attracted to the double bond
  • electrophiles are positively charged so accept a pair of electrons from the double bond
  • a positive carbocation is formed
  • a negatively charged ion forms a bond with the carbocation
• alkenes will burn in air to produce carbon dioxide and water, but they are not used as fuels becuase they are reactive so have more useful purposes
• the positive inductive effect states that alkyl groups have a tendency to release electrons, which stabilises the positive charge of the carbocation
• the more alkyl groups which are attracted to the carbocation, the more stable the carbocation is
• a tertiary carbocation has three alkyl groups attached, this is most stable
• a secondary carbocation has two alkyl groups attached
• a primary carbocation has one alkyl group attached, this is least stable
• the major product will be the most stable carbocation
• common electrophiles are:

  • HBr
  • Br2
  • H2SO4
• addition polymers are made from a monomer or monomers with a carbon-carbon double bond, such as alkenes
• when the monomers are turned into polymers, the double bond breaks to form a carbon-carbon single bond, which means the monomers can be joined together to form a chain
• to draw the single unit of a polymer, draw it with trailing bonds from each terminal carbon and square brackets, include n representing the number of monomers in the chain if necessary
• the reaction conditions used for polymerisation can be changed to give the plastics produced different properties:

  • high pressure and high temperature produces branched chains with weak intermolecular forces
  • low pressure and low temperature produces unbranched chains with strong intermolecular forces
• polymers are unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds
• polymers are useful for manufacturing many products, but are not biodegradable as they do not have any polar regions
• PVC is poly(chloroethene) is an addition polymer with waterproof properties
• the waterproof properties of PVC are developed by adding plasticisers which are small molecules that get between the chains, forcing them apart and allowing them to slide across each other
• PVC is used for many different purposes, including drainpipes, plastic bottles, plastic aprons and packaging
• to name addition polymers, use the prefix poly- and then the monomer in brackets