Alkenes Flashcards
(31 cards)
What is the alkene structure
It is a planar molecule with 120 degree angles
What are the bonds in an alkene
Sigma bond between carbon and hydrogen
One sigma bond between the two carbons
One Pi bond between the two carbons
How is a pi bond formed
In the alkene there are two free electrons on each carbon, they have a P-orbital that overlaps and creates a pi bond
Why are alkenes highly reactive
Pi bonds have a lower bond enthalpy than sigma bonds because the sideways orbital is more unstable that the direct orbital
Why are hydrogen halide molecules attracted to the double bond
They have a permanent dipole and the double bond is an area of high electron density
What is created in the intermediate stage of electrophilic addition
A carbocation and a halogen ion
What is a primary carbocation
A carbocation where the positive charge is on the first carbon (only bonded to one alkyl group)
What is the minor product
The least common product of unsymmetrical electrophilic addition
Why are secondary carbocations more common
The positive carbon is bonded to and stabilised by two alkyl groups so it can survive by itself for longer so is more likely to form a product
How is an induced dipole created in a halogen molecule
The high electron density of the double bond repels the electrons in the halogen molecule bond
How do you test for an alkene
With bromine water, it will go colourless- creating a haloalkene
What is the structure of sulfuric acid
H2SO4
A double bonded oxygen above and below the carbon
An OH on either side of the carbon
Why does H act as an electrophile
The oxygen it is bonded to is very electronegative so the oxygen has slight negative charges and the hydrogen slight positive
What is the first product of an alkene and sulfuric acid
A carbocation intermediate and a hydrogensulfate ion with a negative oxygen
What is the product of a carbocation and a hydrogensulfate ion
Ethylhydrogensulfate (depends on number of carbons for first group)
What does Ethylhydrogensulfate and water produce
Ethanol and sulfuric acid
What is the overall reaction of an alkene and sulfuric acid
Alkene + water –> Alcohol (with sulfuric acid as a catalyst)
How do you get ethanol for Ethylhydrogensulfate
Water takes the place of the hydrogen sulfate
What carbon is hydrogen more likely to bond to in the first stage
The first carbon/ the carbon bonded to the greatest number of hydrogen atoms
What is a polymer
A large molecule made from thousands of small identical molecules called monomers
What are the monomers of addition polymers
Alkenes
What are the conditions of polymerisation
High temperature
High pressure
A catalyst
What happens when an alkene forms a polymer
The double bond opens up and joins one monomer to another
What is the name of polymerised ethene
poly(ethene)
