Module 4: Alkenes (Chapter 13) Flashcards
Define a pi bond
The sideways overlap of adjacent p-orbitals above and below the bonding C atoms. Electron density is localised above and below the plain of the sigma bond. Restricted bond rotation as a result
Bond angle for a double C bond
120 = 3 regions of electron density / 3 bond pairs. Symmetrical molecule giving a trigonal planar shape. Electrons repel as far apart as possible.
Define stereoisomers
Compounds with the same structural formula but a different arrangement of atoms in space.
Define E/Z isomerism
A molecule has a double bond ( no bond rotation) and two different groups are attached to each carbon atom in the double bond.
E isomerism
Opposite sides
Z isomerism
Same side
What is cis/trans isomerism
Special case of E/Z isomerism. One of the groups attached must be hydrogen.
Cis is the same as…
Z isomerism
Trans is the same as…
E isomerism
Describe the Cahn-Ingold-Prelog
Priority given to atom with the highest atomic number on each carbon atom. Z if highest on the same side and E if on different sides.
Why is a sigma bond stronger than a pi bond?
Overlap of orbitals in sigma bonds are end to end and along the line between the two bonding nuclei, whilst pi bond is sideways adjacent overlap, which is poor overlap.
Alkene reactivity
more reactive due to low bond enthalpy of the pi bond as electrons more exposed being on the outside. More readily broken pi bond compared to a sigma bond.
Reactants for hydrogenation
Ni catalyst
423K
H2
Forms an alkane
Halogenation reactants
Halogen added e.g. bromine
Forms a haloalkane
Bromine used to test for double bond = orange to colourless
Hydrogen Halide reactants
Gaseous hydrogen halide e.g. HCl
RTP = 20 and 101kPa
Forms a haloalkane
Hydration reactants
Steam
H3PO4 catalyst
Alcohol forms
Define electrophile
Electron pair acceptor
What type of reaction are addition of molecules to an alkene called?
Electrophilic addition
Markownikoff’s rule?
Primary - tertiary carbocation stability. Determines the major product in a reaction. Increasing number of alkyl groups meaning positive charge more spread over alkyl groups so more stable.
Define monomer
Repeat unit from which a polymer is made
Define polymer
Long chain molecule made up of repeating units of a monomer
Define addition polymer
Long chain molecule formed from many monomer units (containing a double bond) joining end to end. The only product from the reaction.
Benefits to sustainability in polymer disposal?
Combustion for energy production
Use as an organic feedstock for production of plastics and other organic chemicals
Removal of toxic waste products e.g. HCl formed in disposal of PVC
