alkene 14 Flashcards
alkene
unsaturated hydrocarbon
made of carbon and hydrogen only
more reactive than alkane = high concentration of electrons
(Bonding in alkenes involves a double covalent bond, a centre of high electron density)
structure
planar molecule
angle 120 degrees
no rotation around the double bond
double bond can’t rotate
two orbitals overlap to form an orbital with a cloud of electron density above and below the single bond
tips on naming
groups are listed alphabetically
physical properties
van der waals forces are only intermolecular forces
melting and boiling point increase with the number of carbons
not soluble in water
electrophile
electron pair acceptor
react
alkenes more reactive than alkane
electrophilic addition
HBr, H2SO4 and Br2
1 electrophile is attracted to the double bond
2 electrophiles are positively charged and accept a pair of electrons from the double bond.
3 a positive ion is formed (carbocation)
4 negatively charged ion forms a bond with the carbocation
most stable carbocation
tertiary
secondary
primary
test for a double bond
bromine solution (reddish-brown) goes colourless
additional polymers
made of monomers
eg poly(ethene)
use of poly(ethene)
carrier bags
washing up bowls
use of poly(propene)
yoghurt containers
car bumpers
use of poly(chloroethene)
PVC
aprons
vinyl records
drainpipes
use of poly(propenenitrile)
clothing fabrics
use of poly(phenylethene)
packing materials
electrical insulation
(Making poly(phenylethene) from phenylethene.)
modifying plastics
properties can be modified by using additives such as a plasticisers, forcing the chains apart and allowing them to slide over each other
biodegradability
unreactive so are not attacked by biological agents so they are not biodegradable
Low-density polyethene
high pressure and high temperature via free-radical mechanism
the branched chains do not pack together well so its flexible, stretches well and low density
High-density polyethene
temperature and presses little greater than room conditions
Ziegler-Natta catalyst
less chain branching
the chains pack together well
mechanical recycling
separate different types of plastics
plastics are then washed and sorted
make into small pellets
melted and reused
feedstock recycling
heated to a temperature where the bonds will break and used as a new plastics
some materials can be heated a limited number of times because some of the chains break degrading the plastics properties
alkene and oxygen
combustion
would make carbon dioxide and water
alkene and water
hydrolysis CH2=CH2(g) + H2O (g) ---- CH3CH2OH (g) stream pressure acid catalyst suitable temperature
alkene and hydrogen halides
electroplic addition
CH2=CH2 + HCl ——- CH3CH2Cl
alkene and halogens
electrophilic addition
CH2=CH2 + Br2 —- CH2BrCH2Br
dipole caused by getting close to the double bond
Alkenes and concentrated sulphuric acid
electrophilic addition
CH2=CH2 + H2SO4 —— CH3CH2OH + H2SO4
formation of major and minor products
The formation of major and minor products in addition reactions of unsymmetrical alkenes
formations of addition polymers
Addition polymers are formed from alkenes and substituted alkenes.
properties of addition polymers
unreactive
