Alkenes and polymers Flashcards
What are Alkenes
Unsaturated hydrocarbons
Double c=c bond
Alkene general formula
CnH2n
What is a hydrocarbon
Molecule made of carbon and hydrogen atoms only
E-Z isomerism occurs in alkenes due to ….
Restricted rotation around c=c
(Double bond)
Explain CIP priority rules
Look going vertically look for priority group (w highest atomic number) on each side
Then going horizontally if priority group on same side ( Z isomer) if on different side (E isomer)
Test for Alkenes
Adding alkene to bromine water makes it turn from orange to colourless.
The arrangement of bonds around the C=C bond is _____ and the bond angle is around ______
Planar
120-121 degrees
What bonds does C=C bond consist of
One sigma bond
One pi bond
Define steroisomerism
Same structural formula different arrangement of atoms in space
How does pi bond form
Sideways overlap of p orbitals
What part of double bond is stronger sigma or pi bonds
Sigma bonds are stronger
Physical properties of Alkenss
No sig difference in alkenes and alkanes based on mp and bp
Only vdw forces present
Both insoluble in water (cannot form h bonds w it)
Non polar
Combustion of alkenes
Prod co2 and H2O
Not typically used as fuels instead used in chemical reactions
Equation for test for Alkenes using Ethene
Ethene + bromine —> 1.2 di bromo ethane
How does reactivity of alkenes differ from thag of alkasnes
Although c=c bond has lower bond Enthalpy it’s more reactive due to double bind creating an area of high electron density
Thus susceptible from attack by an electrophille
Define electrophille
Electron pair acceptor
It’s an electron deficient species thag attacks and is attracted to areas of high electron density
They add across double bond bc it’s unsaturated
What reaction mechanism do alkenes undergo
Electrophilic addition
Talk though electrophillic addition
Occurs due to heterolutic fission
Non polar br2 approches c=c one br atom gets delta pos charge and other gets delta negative
Arrow from doube bind to delta positive br then from middle of thag bonf to delta neg br cus it takes binfing pair of e
Forms one new c - br and carbon cation
Then arrow from lone pair on br to carbon cation on alkane (double bond broken) then making haloalkane
Explain why there’s an attraction between C=C and Br2 (3)
C=C is an area of high electron density
Br2 becomes polarised/induced dipole
Delta postive br attracted to C=C
3 common electrophilles
Br2
Hbr (hydrogen bromide)
H2SO4 (sulphuric acid)
And reaction w steam
The order of stability for carbocations is
tertirary
secondary
primary
when unsymetrical alkene undergoes addition what products form
major and minor product
what is a carbocation
an ion with positivly charged carbon atom
There are two types of polymerisation…
addititon
condensation
monomers in addition polymeristion
alkenes
c=c double bond
Poly(alkenes) are chemically inert/unreactive bc
due to the strong C-C and C-H
bonds and non-polar nature of the bond and threfore non biodegrsdble
how to draw repeating unit
single c-c bond
extend the bonds on either side of the c-c bond past the brackets surronding
n to the right
if your asked to draw one rep unit wh\t do you do diff
you dont write an n to the right
n rep a large number of rep unit but your only drawing one
why is polychloroethene stronger then polyethene
polyethene only has vdw but pvc has cl so can from stromger perm dipole dipole interactions so thus pvc more stronger and rigid
whats pvc used for
windows
pipes
what makes polymers like pvc more flexible
adding a plasticiser
how do plasticers work
weaken imfs as mol small enough to get in between polymer chains forcing them apart so they can slide over eachother
Markownikkoff’s rule states that the…
the major product will have the hydrogen in the hydrogen halide bond to the carbon atom already bonded to the highest number of hydrogens.
polymers non biodegradable bc
strong c-c bonds
polymers are non biodegrdable so how do we despose of them
burned as fuels
put in landfill
used as chemical feedstock
Where is n on the monomer
On the left
The more stable a carbocation the more …
Alkyl groups it’s joined to
How many alkyl groups in primary secondary and tertiary carbocation
Primary - 1
Secondary - 2
Tertiary - 3
What is the monomer for polyphenylethene
Phenylethene
Are polyalkene chains saturated or unsaturated and why
Saturated with c-c single bonds
What is stronger longer or shorter polymer chains
Longer
Bc the chains can get closer together and thus stronger vdw
Also higher number of electrons
What’s plasticised pvc used for
Electrical cable insulation
