4 Alkenes Flashcards
(16 cards)
Alkenes
unsaturated hydrocarbons
properties of alkenes
boiling point increases as the Mr increases as the number of electron increases, increasing the VdW
Are alkenes water soluble?
No as they are non polar so can’t Hydrogen bond with water
C=C
A centre of high electron density
Combustion of alkenes
they burn in air to produce CO2 and H2O
alkenes burn with a smokey flame
Electrophilic addition to alkenes
double bond of a high electron density attracts electrophiles
addition of hydrogen to alkenes
requires a finely divided nickle catalyst at ~150oC
produces an alkane
addition of halogens or hydrogen halides to alkenes
the delta positive H or X is attracted to the C=C bond
produces haloalkanes
addition of sulfuric acid to alkenes
Hδ+ - Oδ- - SO3H
produces alkyhydrogensulphate, which is easily converted to alcohols through hydrolysis, regenerating sulfuric acid
test for alkenes
add bromine water. If it decolourises an alkene is present
electrophilic addition onto unsymmetrical alkenes
produces more than one possible product
how to determine major product in electrophilic addition onto unsymmetrical alkenes
a carbocation with 3 R groups is more stable than one with 2 R groups or 1 R group. this is because the alkyl (R) groups have a positive inductive effect, pushing the electron density onto the C+
Major product comes from more stable carbocation
addition polymers
formed from alkenes
their double bond breaks and they form a chain.
uses of poly(chloroethene), PVC
strong and hard as C-Cl bonds are polar so there is dipole-dipole interaction between the chains.
used in window frames
use of plasticiser in addition polymers
plasticisers make a polymer flexible as the push the chains apart, weakening the intermolecular forces
poly(phenylethene), polystyrene, uses
food packaging, insulation
