alkenes Flashcards
what are alkenes
unsaturated hydrocarbons with the general formula of CnH2n
what makes alkenes reactive
double bonds have a high electron density
why are alkenes attacked by electrophiles
their double bond and the electrophile adds to the molecule
what are electrophiles
an electron pair acceptor
they are deficient in electrons and are attracted to the double bond
examples of electrophiles
positive charge ions, polar molecules
what is the test for alkenes
addition of bromine- decolorisation of bromine water
bromine is the electrophile and adds to the alkene forming a dibromoalkane
Br is polarised as when come into contact double bond (area with lots of electrons) repels to become polar
electron pair in the double bond attracted to positive bromine and forms bond breaking Br-Br bond
a carbocation intermediate is formed and Br- attracted to positive C
forms colourless 1 2 dibromoethane
alkenes react with hydrogen halides to form …
halogenoalkanes
reactions with .. alkenes produces 2 different products
unsymmetrical
the amount of the 2 products is determined by the … of the … intermediate
stability
carbocation
the more … groups bonded to the carbocation the more stable the intermediate is
alkyl
why do alkyl groups make it more stable
because alkyl groups push electrons towards the positive carbocation stabilising it. the more stable the carbocation the more likely it will form
what is a tertiary carbocation
three alkyl groups pushing electrons towards the carbocation
alkenes react with … sulfuric acid to form…
cold concentrated
alkyl hydrogen sulfates
H2SO4 is used as a … in making an alcohol from an alkene
catalyst
making alcohol from alkyl hydrogen sulfates
adding cold water to warm ethyl hydrogen sulphate will form ethanol- hydrolysis
ethyl hydrogen sulfate => ethanol and sulfuric acid reformed
polymers can be … or …
natural- proteins and natural rubber
synthetic- polyethane and polypropene
what did Charles Goodyear do
discovered vulcanized rubber by adding chemicals to natural rubber to make stronger rubber for tyres
how have polymers been developed for use
polyethane
nylon
teflon
still being made for new tech
how to make polypropene
the monomer propene
the double bond opens up to form polymer
polyalkenes properties
saturated so normally non polar and hence unreactive
but that means they don’t degrade well in landfill
intermolecular forces in polymers
most have only van der waals forces
the longer the chain the more van der waals as they can pack together closer giving higher bpt and are rigid and stronger
shorter more branched chains are more flexible and weaker
polyalkenes with halogens intermolecular forces
they can also now form stronger permanent dipole dipole forces eg-PVC
what are plasticisers
are added to polymers to change properties making it more flexible
how do plasticisers work
they slide between the polymer chains pushing them apart
this weakens the imf and the chains can now slide over each other making it easier to bend
