FC17 - Alkenes Flashcards
Define stereoisomerism
Compounds with the same structural formula but different arrangements of atoms in space
What do you need for e/z isomerism
A carbon to carbon double bond and each of the doubly bonded carbon atoms must be bonded to 2 different types of atoms/groups
What are the CIP rules
1: for each doubly bonded C, the atoms bonded are assigned “ priorities “ (using atomic number)
2: if the higher priority groups are on the same side of the double bond, then we have a Z-isomer, if they are on either side of the bond, E-isomer
Define cis-trans isomerism
To get from one H to the other H, if you have to transverse across the double bond then it is a trans-isomer, if not, then it is a cis-isomer. Same applies for if you have two identical groups rather than 2 hydrogens
How can you prepare alkenes from the dehydration of alcohols
Alcohol + heat and concentrated sulfuric acid = alkene and water
Elimination reaction - can only occur if the hydroxyl group is bonded directly to a C atom that is bonded to an adjacent C atom, which is directly bonded to H
What are the 4 types of addition reactions of alkenes and state the conditions
1- halogenation using a halogen
2- halogenation using a hydrogen halide
3- hydrogenation (requires heat and a Platinum or nickel catalyst) - of vegetable oils to make margarine
4- hydration (requires steam at 300 degrees and phosphoric acid catalyst, 60 atm)
Describe the electrophilic addition mechanism and also about what happens when using a halogen
Double c=c bond is an electron rich region and so partial positive (hydrogen) attracts electrons from double bond - if using halogen to halogen, induced dipole is made as electron rich region of double bond repels electron around halogen downwards - this pair of electrons repel the pair between (hydrogen and bromine) and so those electrons get pushed to the partial negative (bromine) making it negative. One of the carbons from the double bond, bonds to (hydrogen), other carbon is now a carbocation intermediate as it has lost one bond to become a positive bond. Electron pair from negative bromine ( :Br- ) is attracted to positive carbon ion.
What is an electrophile
An electron pair acceptor
How are sigma bonds formed?
Formed by the direct overlap of orbitals
How are pi bonds formed?
By the sideways overlap of p-orbitals, above and below the sigma bond is one pi bond.
Why is rotation not possible around a double bond
Rotation of the double bond would cause the sideways overlap between the p orbitals of the pi bond to be disrupted and hence break the pi bond
What is the template explanation for why there is a major and minor product in an alkene addition reation
X is the major product as it is formed from the more stable secondary/tertiary carbocation intermediate, whereas the alternative product is formed from the less stable primary/secondary carbocation intermediate, and so the yield of the major product is higher than that of the minor product
How can alkenes form addition polymers
through an addition reaction
How are polymers recycled
discarded polymers are sorted by type, then chopped into flakes, washed, dried and melted. Recycled polymer is cut into pellets and used to make new products
How is recycling polymers beneficial for the environment
conserving finite fossil fuels, decreasing waste going to landfill
Why is recycling PVC hazardous (polychloroethene)
when burnt, releases hydrogen chloride - corrosive gas and other pollutants like toxic dioxins
What happens to waste PVC, as recycling is hazardous
dissolved in solvents, then high grade PVC is recovered by precipitation from the solvent, solvent is used again
How can waste polymers be used as fuel
Can be incinerated to produce heat, generating steam to drive a turbine producing electricity
What is feedstock recycling of polymers
chemical and thermal processes that can reclaim monomers, gases or oil from waste polymers. Can be used as raw materials for production of new polymers. Able to handle unsorted and unwashed polymers
What are biodegradable polymers
broken down by microorganisms into water, carbon dioxide and biological compounds. These polymers are made from starch of cellulose, or have additives that altar their structure
What are photodegradable polymers
oil based, contain bonds that are weakened by absorbing light to start the degradation.
What are the conditions and reagents needed for hydrogenation of alkenes
heat and Pt or Ni catalyst
What are the conditions and reagents needed for hydration of alkenes
steam, 300 degrees celsius, phosphoric acid catalyst, 60 atm
What does hydrogenation of vegetable oils make
margarine
