Alkenes
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- Created by: RIPClubPenguin
- Created on: 14-04-17 14:22
What kind of hydrocarbon are alkenes?
Unsaturated
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What makes alkenes different from alkanes?
They can contain carbon=carbon double bonds
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What 2 types of bonds is a carbon carbon double bond made of?
A sigma bond and a Pi bond
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What forms a sigma bond?
Overlap of orbitals between bonding atoms
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What forms a Pi bond?
Overlap of adjacent P orbitals
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The pi bond is an area of ..?.. electron density above and ..?.. the plane of the molecule
High, below
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What does the Pi bond prevent the double bond doing?
Rotating about its axis
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What are the bond angles around the carbon carbon double bond in an alkene?
120 degrees
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What is the general formula of an aliphatic alkene?
CnH2n
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What other organic homologous series has the general formula CnH2n?
Cycloalkanes
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What does the name of an alkene end in?
Ene
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What is the general formula of cycloalkenes?
CnH2n-2
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What is stereoisomerism?
Molecules have the same structural formula but with a different arrangement in space
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What type of stereoisomerism can some alkenes show?
E/Z isomerism
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What two conditions have to be met for E/Z isomerism?
Double bond can't rotate about its axis (due to pi bond in alkenes) and have two different groups at each end of the carbon carbon double bond
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What is the name of the type of E/Z isomerism in which at each end of the double bond, there is one non-hydrogen group and one hydrogen atom?
Cis-trans isomerism
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Which of either Cis or Trans does the non hydrogen group go diagonally across the double bond?
Trans
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What makes a group have a high priority in cis-trans isomerism?
The higher the atomic number
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Why do alkenes react?
Pi bond has low bond enthalpy
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Which bond is broken more readily when alkenes undergo addition reaction?
Pi bond as it is weaker
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What is a test for alkenes and what is positive result?
Add bromine water and if alkene is present, it turns colourless
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What is the addition of halogens called?
Halogenation
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What are the reagents and conditions for halogenation?
Br2/Cl2 and room temperature
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What happens in halogenation?
Carbon carbon double bond breaks and reagent adds on to each carbon
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What is the reagents and conditions needed in addition of hydrogen halides?
HCl/HBr/HI and room temperature
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What happens if an unsymmetrical alkene is used in addition of hydrogen halides?
2 possible products form which are isomers of each other
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What is the addition of hydrogen called?
Hydrogenation
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What are the conditions and catalyst needed for hydrogenation?
High pressure and High temperature (150 degrees celsius) and nickel catalyst
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What is the product in hydrogenation reactions?
Alkanes
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What is the addition of steam also known as?
Hydration
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What are the conditions and catalyst needed for a hydration reaction?
High temperature and high pressure, and phosphoric acid (H3PO4)
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What product is made in a hydration reaction?
Alcohol
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Define polymerisation
joining of monomers to form a polymer
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What type of polymerisation occurs in polymerisation of alkenes?
Addition
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How many repeat units are there in addition polymers and how many products?
1 and 1
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What is a benefit of addition polymers and why?
Cheap - made from oil derived raw materials
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What are two disadvantages of additions polymers and why?
Non-renewable source (come from oil derived raw materials), Non-biodegradable (issues if disposed of via landfill)
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What are some uses of waste polymers?
Combust for electricity production and use as organic feedstock for production of other plastics and organic chemicals
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What are some problems with using waste polymers as fuels?
Release greenhouse gases when burnt and halogenated plastics release toxic gases (e.g HCl) that needs scrubbers to remove
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What are bioplastics made from?
Plant starch, cellulose and plant oils
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Where are biodegradable polymers broken down and by what?
Environment, living organisms
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What are photodegradable polymers broken down by?
Absorption of light
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What are 2 benefits of biodegradable polymers and photodegradable polymers?
Degradable (can be disposed of by landfill) and renewable
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What are 2 examples of electrophillic addition reactions?
Alkenes with bromine / hydrogen bromide
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What is an electrophile, what is its charge and what is it attracted to?
An electron pair acceptor, positive, and the high electron density of the pi bond in a C=C double bond
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What is a carbocation and when is it formed?
Positive ion with an electron deficient carbon, formed as an intermediate in electrophillic addition reactions
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What type of bond breaking occurs in electrophillic addition reactions?
heterolytic fission
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What are two products of heterolytic fission bond breaking?
Cation and anion
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What happens when HBr bond breaks through heterolytic fission
H+ Br-
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In the addition of bromine, what indices a dipole in Br2 molecule?
Electron rich double bond
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What is the electrophile in the addition of Bromine and what does it do?
Br+, accepts the pair of electrons of the pi bond causing the pi bond to break and new c-br covalent bond to form
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What does the Br-Br bond break from?
Heterolytic fission
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What intermediate is formed?
A carbocation
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What uses its lone pair of electrons to form a second C-Br covalent bond?
Bromide ion
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In the addition of hydrogen bromide (which is basically the same as Bromide) what acts as the electrophile?
Hydrogen
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What two things have to react for Markwonikoff's rule to be used?
An unsymmetrical alkene and an unsymmetrical molecule e.g HBr
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What does Markownikoff's rule allow you to do?
Predict which of the two possible isomers is going to be the major product
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What are the three types of carbocations in order of stability from highest to lowest?
Tertiary, Secondary and Primary
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What is classed as a R group?
Anything that isn't a hydrogen atom
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How many R groups does tertiary, secondary and primary carbocations have?
3,2,1
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The least stable product is going to be the major product. True or false?
False
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Other cards in this set
Card 2
Front
What makes alkenes different from alkanes?
Back
They can contain carbon=carbon double bonds
Card 3
Front
What 2 types of bonds is a carbon carbon double bond made of?
Back
Card 4
Front
What forms a sigma bond?
Back
Card 5
Front
What forms a Pi bond?
Back
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