topic 6c: alkenes Flashcards
general formula alkene
cnh2n
alkene description
unsaturated hydrocarbon
c=c bond consists of (interms of bonding)
one sigma
one pi bond
how is a sigma bond formed
1 sp2 orbital from each carbon overlaps to form a single c-c sigma
how is a pi bond formed
sideways overlap of 2 p orbitals on each C. pi bond formed above and below the plane of the molecule
RESTRICTED ROTATION
is pi or sigma stronger
SIGMA
PI BOND ELECTRON DENSITY
- high ed
- above and below the line between the 2 nuclei
ELECTROPHILE
electron pair acceptor
- pi bonds are vulnerable to attack by them because theyre exposed w high electron density
alkene + hydrogen
- addition
- nickel catalyst
-forms alkane
alkene + halogen
- halogen reagent
- room temp
- forms dihalogenoalkane
alkene + hydrogen halide
- hydrogen halide reagent
- room temp
forms alogenoalkane
alkene + ACIDIFIED potassium manganate (VII)
- KMnO4 reagent in an acidified solution
- room temp
- OXIDATION
- forms a diol
PURPLE MnO4- COLOUR GONE, to colourless mn2+
bromine water + alkene
reagent: bromine dissolved in water
- addition
- bromine water decolourises from orange to colourless
alkene + steam
- acid catalyst - CONCENTRATED H3PO4
- High temp 300-600
- high pressure 70 atm
- hydration
- alcohol
what does heterolytic bond fission form
ions
addition polymers are formed from …
alkenes
why are polyalkenes unreactive
strong c-c c-h bonds
recycling of polymers
- saves raw materials
- polymers need sorting/collecting
- careful separation needs to be done. can only be recycled into the same type
incineration of waste polymers
- burnt and energy produced genrates electricity
- releases toxins, greenhouse gases
- reduces volume of rubbish
waste polymers as feedstock for cracking
- polymers cracked into small molecules used to make other things
- saves raw materials
2 ways chemists limit the problems caused by polymer disposal
- developing biodegradable polymers
- removing toxic waste gases caused by incineration of plastics
biodegradable polymers
- can biodegrade
- made from maize + starch
how do chemists remove the toxic waste gases caused by the incineration
waste cases reacted with a base/carbonate. neutralises it
why is the empirical formula of the polymer the same as that of the repeating unit
- addition polymerisation
- no small molecules formed
atom economy of addition polymerisation
100%
- addition polymerisation
- no small molecules formed (no co products)
