4.1.3 alkenes

CnH2n

C=C double covalent bond has one sigma and one pi bond Pi bonds are exposed and have high electron density Electrophiles are attracted to them

Sideways overlap of two p orbitals on each atom Forms a pi bond above and below plane of molecule Pi bond weaker than sigma

Alkene > alkane Reagent: Hydrogen Nickel catalyst Addition reaction

Alkene > dihaloalkane Reagent : bromine/chlorine Conditions: room temperature Electrophilic addition Heterocyclic bond fission

Alkene > haloalkane Reagents: HCl or HBr Conditions : room temperature Electrophilic addition H+ dipole attracted to electron-rich pi bond , Br more electronegative so polar HBr

Alkene > alcohol Reagents: steam High temperature (300-600C) High pressure 70atm Catalyst of concentrated H3PO4 Aka hydration

Formation of polymers from ethene based monomers Manufacture of margarine by catalytic hydrogenation of unsaturated vegetable oils using H2 and nickel catalyst

Separation and recycling - waste sorted then each type can be recycled by melting and moulding Feedstock for cracking - waste polymers used as feedstock for cracking process allowing for production of new plastics Combustion for energy production - incinerated and heat released used to generate electricity - combustion of halogenated plastics (PVC) can lead to formation of toxic waste products e.g. HCl

electron pair acceptor

electron pair donor

two sp2 orbitals (one from each carbon) overlap to form a single C-C bond called a sigma bond

same structural formulae but different spatial arrangement of atoms

exist due to restricted rotation about C=C bond also arise when 2 different groups/atoms attached both ends of the double bond

determine priority groups on both sides of the double bond (atom with bigger atomic number) if priority group is on same side of double bond it is labelled Z, if not then E

higher boiling point polar molecule : polar bonds on same side of molecule so one side of the molecule is slightly negative london forces and permanent dipole-dipole interactions

lower boiling point non-polar: polar bonds on opposite sides of the molecule so dipoles cancel out only london forces so lower BP

bromine will be added to carbon with fewest hydrogens attached to it > major product formed via more stable carbocation intermediate - tertiary > secondary > primary major & minor products