Unit 3,2,9 - Alkenes Flashcards
What are alkenes?
Unsaturated hydrocarbons containing C=C bonds.
What is the arrangement and the bond angle between a C=C bond?
Planar arrangement - 120.
What are stereoisomers?
Molecules with the same molecular formula and the same arrangement of covalent bonds but different arrangement in space.
Why can alkenes present stereoisomerisms?
They can’t rotate about the double bond.
What are the two types of isomers within stereoisomerism?
E and Z
What are E isomers?
When the groups are attached on opposite sides of the double bond.
What are Z isomers?
When the groups are attached together on the same side of the double bond.
Draw an E and Z isomer of dichloroethene
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Why can a double bond attract electrophiles?
The double bond is a centre of high electron density so has a slightly negative charge.
What is an electrophile?
Electron pair acceptors.
Give three examples of electrophiles?
Halogens, Hydrogen Halides, Sulphuric Acid.
What type of reaction do alkenes go under with electrophiles?
Electrophilic Addition
Draw the mechanism for the electrophilic addition between Ethene and a Halogen.
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Draw the mechanism for the electrophilic addition between Ethene and Hydrogen Halide.
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Draw the mechanism for the electrophilic addition between Ethene and Sulphuric Acid.
See Flash Card
How can we test for the presence of Alkenes and what are the results you would expect?
Mix the solution with orange bromine water.
In the presence of an Alkene it will turn from orange to colourless.
Why does Bromine water turn colourless in Alkenes?
Bromine is added to the double bond by electrophilic addition forming a colourless dibromoalkane.
During electrophilic addition, which product is most likely to form?
One where the carbon holding the carbocation is attached to the most other carbon atoms.
What two methods are there for producing alcohols?
- ) Steam hydration of ethane
2. ) Hydrating alkenes in the presence of an acid catalyst
Name three conditions for when ethane is hydrated by steam to produce ethanol.
300C
60atm
Solid Phosphoric Acid Catalyst
What is the first step when alkenes are hydrated to alcohols?
They are reacted with concentrated Sulphuric Acid
How are alkenes hydrated to alcohols?
They are reacted with water in the presence of cold concentrated sulphuric acid.
What is the overall equation for when ethane is hydrated to ethanol?
……..
What is addition polymerisation?
Alkenes are joined up together under high pressure with a suitable catalyst.
