alkenes

type of isomerism in alkenes

positional

what does C=C double bond consist of?

one sigma and one pi bond

properties of pi bonds

exposed and high electron density
vulnerable to attack by species of ‘like’ electrons - electrophiles

is a pi bond or sigma bond stronger

sigma

bond angle around C=C bond

trigonal planar - 120 degrees

E/Z stereoisomerism

exists due to restricted rotation around C=C bond
2 different atoms/groups attached to each C in double bond

cis/trans isomerism in alkenes

special case of E/Z isomerism where 2 of the groups are the same

effect of E/Z stereoisomerism on physical properties

Z: polar because polar bonds are on the same side - one side of molecule is slightly negative
E: non-polar because polar bonds are on opposite sides of the molecule so cancel out (lower boiling point)

reactivity of alkenes

relatively reactive due to low bond enthalpy of pi bond

reactivity of poly(alkenes)

unreactive due to strong C-C and C-H bonds

benefits for sustainability of processing waste polymers

combustion for energy production
use as organic feedstock for production of plastic
removal of toxic waste products (HCl)