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
