Alkenes

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  • Created by: Kate
  • Created on: 18-02-14 16:18
What is an Alkene?
Unsaturated hydrocarbons. They are made up of carbon-carbon double bonds
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What is the general formula for Alkenes?
CnH2n
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What are Stereoisomers?
Molecules with the same molecular formula and the same arrangement of covalent bonds but with different spacial orientations of the groups
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What are Geometrical Isomers?
Stereoisomers with with different spatial orientations around the carbon-carbon double bond. It is caused by the restricted rotation about a carbon-carbon double bond.
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When does geometrical isomerism occur?
When the carbon atoms on both sides of the bonds are attached to two different groups.
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When distinguishing Geometrical Isomers, what two prefixes are used?
E (entgegen) -opposite Z (zusammen) -together
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When would you expect to see E as a prefix on a geometric isomer?
When the hydrogen atoms are on different sides of the molecule
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When would you expect to see Z as a prefix on a geometric isomer?
When both the hydrogen atoms are on the same side of the molecule
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What two structural features must a molecule have to have geometrical isomerism?
1) Carbon-Carbon double bond 2) both carbon atoms are attached to two different groups
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How should geometrical isomerism always be drawn?
using crab notation
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What is Crab Notation?
A method of showing Geometrical Isomerism. The C=C bond is a planar centre with four groups.
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Which is more reactive: Alkanes or Alkenes?
Alkenes - because of the C=C
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Explain in terms of electron density why Alkenes are more reactive
The C=C has a high electron density which means that it may be easily attacked by positively charged reagents (eg electrophiles)
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What is the most common reaction of Alkenes?
Electrophillic Addition
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Define a polymer
a long chained molecule made up of many monomers joined together by single bonds (unsaturated)
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What is addition polymerisation?
formation of a long chain molecule from lots of monomers with no other products
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What is an electrophile?
electron pair acceptors, they are attracted to negative charge
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Define carbocation
an organic ion containing a positively charged carbon atom
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In an electrophillic addition reaction, why is it that a secondary carbocation is more stable than a primary carbocation?
A secondary carbocation has two methyl groups releasing electrons towards the positive carbon. The more electron density pushing on the positive carbon (carbocation) the more stable it will be.
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Card 2

Front

What is the general formula for Alkenes?

Back

CnH2n

Card 3

Front

What are Stereoisomers?

Back

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Card 4

Front

What are Geometrical Isomers?

Back

Preview of the front of card 4

Card 5

Front

When does geometrical isomerism occur?

Back

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