alkenes Flashcards
double bond
one sigma one pi bond
pi bond makes C–C unable to rotate
-gives it fixed shape around the bond
- involves electrons in p orbitals to exist above and below plane of bond- no overlapping (unlike sigma)
bond angles around C–C bond
three regions of negative charge
repel equally
120 degree angle
all in same plane
stereoisomerism
possible due to double bond
rigid- cannot rotate around them
displayed at stereoisomerism
e- large groups on different sides
z- large groups on same side
alkenes
react in additon reactions
alkenes are nucleophiles- high electron density between carbon atoms
cahn ingold
four directly connecting atoms ordered by atomic mass
highest AM gets priority 1
uses of electrophilic addition
bromine- test for alkenes ( orange -> colourless in alkene)
bromine added to alkene via electrophilic addition
sulphuric acid + water- produces alcohols
- alkene + sulfuric acid= alkyl hydrogen sulfate –> diluted and distilled with water to produce an alcohol
sulfate ion removed by nucleophilic subsititution
asymmetric electrophilic addition
multiple products could be produced
selectivity- one will be favoured over the other
intermediate stability
- driven by CARBOCATION INTERMEDIATE STABILITY
tertiary> secondary> primary carbocations
more alkyl groups next to positive charge, more stable the intermediate is
alkyl groups push electrons - help stabilise adjacent positive charge
choosing product
consider intermediates formed
both will be formed but one major one minor
MOST STABLE carbocation will be major
electrophilic attack
electrophile much have pos/ partial pos charge to be attracted to regions of neg charge
involves mechanism of heterolytic fission of electrophile molecule
electrophilic attack 2
pos end attracted to electron dense region in C–C bond
- pi bond electrons attracted towards H and form covalent bond
addition of negative ion
electrons from C–C bond covalently bonding with H atom
one carbon atom has pos charge now- carbocation
poly(ethene)
high density- linear chains
low density- branched chains (flexible)
used in plastic bags,bottles, toys
poly(chloroethene)
can be made flexible or rigid
used for pipes sheeting insulation cables
poly(propene)
toys guttering windows
poly(phenylethane)
packaging material/food trays
cups
poly(tetraflouroethane)
coating non stick pans
cable insulation
lack of polymer reactivity
hard to dispose of
most are not biodegradable
recycling polymers
conserves fossil fuels
decreases waste in landfill
method recycling polymers
sorted by type
chopped into flakes
washed and dried
melted
cut into pellets
used to make new products
disposal/ recycling pvc
hazardous- high chlorine content + additives
release HCl when burnt + other toxic gases
high stored energy value- can be burnt to produce heat- steam turns turbine to produce electricity
feedstock recycling
chemical and thermal processes reclaim monomers from waste polymers
used as raw materials to produce new polymers
able to handle unsorted unwashed polymers
bioplastics
produced from plant starch, cellulose, plant oils and proteins
renewable + sustainable
biodegradable polymers
broken down –microorganisms—> water + CO2 + biological compounds
used as bin liners for food waste so both compost
photodegradable polymers
oil based
bonds weakened by absorbing light to start degradation OR light absorbing additives used
