Ch13 Alkenes Flashcards
What is an alkene?
Alkenes are unsaturated hydrocarbons that contain at least 1 C=C bond (functional group).
Alliphatic alkenes w/ 1 = have general formula CnH2n
Alkenes can be branched, cyclic and contain 1+ double bond.
What is an alkene?
Alkenes are unsaturated hydrocarbons that contain at least 1 C=C bond.
Alliphatic alkenes w/ 1 = have general formula CnH2n
Alkenes can be branched, cyclic and contain 1+ double bond.
Explain sigma + pi bond
Explain the formation of the double bond in alkenes:
C=C double bond is comprised of a sigma bond (σ) and a pi bond (π).
σ bond: formed by overlap of orbitals directly between bonding carbon atoms.
π bond: formed by sideways overlap of adjacent p-orbitals above and below bonding C atom.
Define Stereoisomers:
Stereoisomers are compounds with the same structural formula but different arrangement of atoms in space.
Why do E/Z stereoisomers occur?
E/Z isomerism around C=C arises due to the restricted rotation around double bond which fixes the group attached to each C atom in position.
Rigidity of double bond due to π bon’s electron density being concentrated above and below the plane of σ bond.
What conditions permit the occurence of an E/Z isomer?
2 conditions must be met:
1. C=C double bond
2. different groups attached to each C atom of double bond.
Describe E/Z isomerism:
Why are alkenes more reactive than alkanes?
Alkenes are more reactive because the π bond is weaker than σ bond, as π requires less energy to break.
When alkenes react, π bond breaks but σ bond remains intact.
What kind of reaction do alkenes undergo?
Alkenes undergo electrophillic addition reactions
draw
Describe the hydrogenation of alkenes:
Describe the halogenation of alkenes:
What is the test for unsaturation in alkenes?
Describe the addition of hydrogen halide to alkenes:
Describe the addition of hydrogen halide on unsymmetrical alkenes:
Describe the hydration of alkenes:
Describe the addition of steam to unsymmetrical alkenes:
Define ‘Electrophiles’:
Electrophiles - electron pair acceptors.
Usually + ions/molecules where one of the atoms has partial positive charge.
Draw the mechanism for electrophillic addition of bromine to an alkene:
What is Markownikoff’s Rule of carbocation?
When an unsymmetrical alkene reacts with an unsymmetrical molecule, there are 2 possible isomeric products.
1st step of mechanism- carbocation is formed as intermediate (stage)
The major product will be formed from more stable carbocation
What are the 3 different classifications of carbocations?
Describe and explain the differing stability of carbocations:
Draw the mechanism for electrophillic addition of an unsymmetrical molecule to an unsymmetrical alkene:
What is addition polymerisation?
- Polymerisation is carried out at high temperatures and pressures using catalysts.
- A polymer is a large molecule formed from many thousands of repeat units of smaller molecules known as monomers.
- Place bracket around one unit and add ‘n’ next to it for repeating units.
What is the structure and different uses of Poly(ethene)
What is the structure and different uses of Poly(propene)?
What is the structure and different uses of Poly(chloroethene)?
What is the structure and different uses of poly(phenylethene)?
What is the structure and different uses of Poly(tetrafluoroethene)?
Why are polymers of alkenes a cause for environmental concern?
- Alkene-based polymers: non-biogradeable, so there are problems for safe disposal.
Describe ‘Recycling’ as a method of polmer waste disposal:
- Involves sorting polymer waste into different types before chopping into flakes, washing, drying, melting + reshaping for repurposing.
- Conserves finite fossil fuels and decreases amount of waste sent to landfill
What is a problem of disposing PVC?
- PVC contains range of additives and high Cl content
- Sending to landfill not sustainable
- Burning PVC releases corrosive HCl gas and other pollutants
- e.g. toxic dioxins
- PCV polymers are now recycled by dissolving in solvents and recovering them from solvent by precipitation.
Describe ‘using waste polymers as fuel’ as a method of reusing polymers:
- polymers can be incinerated to produce heat + generate steam to drive turbines and produce electricity.
Describe using waste polymers as organic feedstock as a method of reusing polymers:
- Chemical + thermal processes can be used to reclaim monomers, gases or oil from waste polymers.
- Reclaimed products can be used as raw materials for production of new polymers
- Feedstock recycling advantage: being able to handle unsorted + unwashed polymers
What are bioplastics?
- Bioplastics are biodegradable polymers produced from plant starch, celulose, plant oils + proteins.
- Bioplastics are renewable and sustainable.
- Can be broken down by microorganisms into water, CO2, and biological compounds.
- Bioplastics help protect environment + conserve valuable oil reserves
What are photodegradable polymers?
- Photodegradable polymers contain bonds that weaken when light absorbed - start process of degradation.
