Chemistry - Alkenes

• Alkenes are unsaturated hydrocarbons that contain at least one C=C bond made up of a pi bond and a sigma bond
• The general formula of alkenes is CnH2n
• A pi bond is formed when electrons in the adjacent p orbitals overlap above and below the carbon atoms, after a sigma bond is formed
• The π bond restricts the rotation of carbon atoms
• The angle and shape of a double bond is trigonal planar with an angle of 120 degrees
• Alkenes are more reactive than alkanes due to the high electron density of the double bond and the fact that the pi-bond is slightly easier to break
• Alkenes have only London forces as intermolecular forces of attraction due to non-polar bonds
• Alkenes are not soluble in water due to non-polar bonds
• The complete combustion of pent-2-ene is: CH3CHCHCH2CH3 + 7(and a half)O2 → 5CO2 + 5H2O
• Types of isomers that can be formed using alkenes are E/Z isomers and cis-trans isomers
• An electrophile is a species that are electron pair acceptors
• The most stable type of carbocation intermediate is a tertiary carbocation due to the positive inductive effect of alkyl groups
• Major products will be formed from tertiary (or the most stable available) carbocations
• Conditions needed for the electrophilic addition of H2O to an alkene are steam in the presence of an acid catalyst, usually phosphoric acid. This reaction is called hydration
• The product of the hydration reaction is an alcohol
• Conditions needed for the electrophilic addition of a hydrogen halide to an alkene are that hydrogen halide gases must be at room temperature
• The reaction when a halogen is added to an alkene is called halogenation
• A molecule with a non-polar bond reacts as if it is an electrophile due to the C=C double bond inducing a temporary dipole in the halogen molecule
• An alkene can be converted into an alkane through hydrogenation with conditions of 150 degrees celsius and a nickel catalyst
• An addition polymer is formed when many monomers are bonded together via rearrangement of bonds without the loss of any atom or molecule
• Monomers are molecules that combine to form a polymer and usually have a C=C bond which breaks to leave a repeating pattern
• Ways in which plastics can be disposed are landfill, combustion, electricity generation, reuse, recycle, and organic feedstock
• Disadvantages of recycling include the need to sort plastics into different types, expense, labor intensiveness, and the requirement of high technology
• Photodegradable polymers break down chemically using energy with wavelengths similar to light, and once the breakdown begins, it cannot be stopped
• In organic feedstock, plastics are separated and broken down into small organic molecules through a series of reactions to be used in producing plastics and other industries
• A disadvantage of photodegradable polymers is that they may not be exposed to sufficient light