4.1.3 alkenes Flashcards
what are alkenes
unsaturated hydrocarbons
what is the general formula of alkenes
cnH2n
what is the molecule shape around the alkene carbons and what is the bond angle
trigonal planar
120
what is a sigma bond
a bond formed when two s orbitals overlap. the
what is a pi bond
a pi bond is formed by the sideways overlap of two p orbitals
why is a sigma bond stronger than a pi bond
high electron density between nuclei means there is a strong electrostatic attraction between nuclei and shared pair. this gives sigma bonds high enthalpy. in a pi bond the electron density is spread out so it is weaker
why are alkenes more reactive than alkanes
the pi bond from the c=c stick out slightly above and below the bond and attacked by electrophiles
what are stereoisomers
they have the same structural formula but a different arrangement of atoms in space
what are E/Z isomers and what causes them
stereoisomers occur because the double bond cannot rotate.
E isomers have highest priority groups on opposite sides
Z isomers have the highest priority groups on the same side
what groups are given priority in E/Z isomerism
highest atomic number has priority
what are cis/trans isomers
stereoisomers when the carbon atoms have at least one group in common
cis - same groups are on the same side
trans - same groups are on opposite sides
what is electrophilic addition
the double bond opens up and atoms are added to the carbon atoms
what are the reagents/ condition to produce alkanes from alkenes
hydrogen (H2)
nickel catalyst and 150 degrees
what are the reagents/ condition to produce dihaloalkanes from alkenes
halogens (X2)
room temperature
how can we test for the carbon-carbon double bond
shaking with bromine water causes a colour change from orange to colourless
what are the reagents/ condition to produce haloalkanes from alkenes
hydrogen halides (H-X)
room temperature
how doe we determine the major product
the most stable carbocation forms most of the time which forms the major product
what is markownikoff’s rule
the major product from addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached
what are the reagents/ condition to produce alcohols from alkenes
steam
300 degrees
60-70 atm
H3PO4 catalyst
how do alkenes form polymers
the double bond opens up and bond to multiple monomers. this is called addition polymerisation
why are polymers useful
they are unreactive and cheap to produce
what is a limitation of polymers
they are hard to dispose of
what is the advantages and disadvantages of land fill
it can pollute the land and takes up lots of space
it wastes the polymers
it is cheap and easy and quick
what is the advantages and disadvantages of reusing polymers
we have to sort them which takes time
it and their properties are reduced for each reuse
what is the advantages and disadvantages of burning polymers
it releases emissions and sometimes toxic gases
it can be used as an energy source
what is a biodegradable polymer
a polymer that degrades pretty quickly in certain conditions
what are biodegradable polymers made of
renewable raw materials such as starch
what is a photodegradable polymer
polymers that decompose when exposed to sunlight
