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Organic Chemistry > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What is the general formula for alkanes

A

Cn H2n

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2
Q

What type of hydrocarbons are alkenes

A

Unsaturated hydrocarbons because they captain at least one double covalent bond between the carbon atoms

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3
Q

Alkenes will generally have less what?

A

Hydrogens

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4
Q

Why are C=C bonds unsaturated

A

Because they make more bonds with extra atoms in addition reactions

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5
Q

How many pairs of electrons are found in C=C and what does this result to?

A

• Two pairs of electrons
• High electron density
• Makes alkenes reactive

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6
Q

What type of alkene would have 2 Hs less than the equivalent open-chain alkene

A

Cyclic alkenes

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7
Q

What type of addition reaction happens with alkenes?

A

Electrophilic addition reactions

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8
Q

How do electrophilic addition reactions happen?

A

The double bonds open up and atoms are added to the carbon atoms

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9
Q

Why do electrophilic addition reactions happen?

A

The double bond has got plenty of electrons and is easily attacked by electrophiles

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10
Q

What are electrophiles

A

Electron pair acceptors

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11
Q

What charge do electrophiles carry and why?

A

Positive charge because they are short of electrons

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12
Q

What is used to test for in saturation

A

Bromine water

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13
Q

Describe the test for unsaturation

A

• Shake an alkene with orange bromine water
• The solution quickly decolourises
• Colourless dibromoalkane
• Via electrophilic addition

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14
Q

Name two compounds Alkenes undergo Electrophilic addition with

A

• Hydrogen halides
• Sulphuric acid

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15
Q

What is formed when alkenes react with hydrogen bromide?

A

Halogenoalkanes

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16
Q

Adding hydrogen halides to unsymmetrical alkenes form what two products

A

A stable (major product) and an unstable Carbocation (minor product)

17
Q

What is the difference between a stable product and an unstable product

A

A stable product will have more alkyl groups so it will be produced more

18
Q

What are the three type of carbocations?

A

Primary, secondary and tertiary

19
Q

Draw the mechanism for the reaction of propene with hydrogen bromide

A

Check physical flashcards for answers

20
Q

What conditions are required to react alkenes with sulphuric acid and what product is formed?

A

• Cold concentrated sulphuric acid
• Alkyl hydrogen sulphates

21
Q

How are alkyl hydrogen sulfates formed into alcohols?

A

• Add cold water and warm the product
• It hydrolyses to form an alcohol
• The sulfuric acid is not used up, so it acts as a catalyst

22
Q

Draw the mechanism for the reaction of ethene with sulfuric and cold water to form an alkyl hydrogen sulfate and an alcohol

A

Check physical flashcards for answers

23
Q

What is carbocation

A

An organic ion containing a positively charge carbon atom

24
Q

What is the iupac name of the major product of the reaction between 2-ethylbut-1-new and hydrogen bromide

A

3-bromo-3-methylpentane

25
Q

Give the formula for percentage yield

A

Actual yield/Theoretical yield x100

26
Q

Give the formula for atom economy

A

Mass of useful product/total mass of product x 100

27
Q

State the importance of percentage yield and atom economy when choosing the method used to make a compound

A

• Yield: so you can use less starting material, reactants

• Economy: So makes less (waste) product

28
Q

What areas are electrophiles attracted to?

A

electron rich areas

29
Q

When do addition reactions occur?

A

Where there is a double bond

30
Q

Explain why there is an attraction between a C=C double bond and Br2

A

• Double bond in C=C is electron rich
• Brs+ is attracted to to C=C
• Br-Br becomes polarised

31
Q

What is the difference between addition polymerisation and condensation polymerisation

A

• In addition polymerisation, monomers are added together with no by-products, while in condensation polymerisation, monomers react with each other and release by-products like water or methanol

32
Q

Give the conditions needed to favour an elimination reaction

A

• Alcoholic/ethanolic solvent
• Hugh temperature
• Hot under reflux

33
Q
  • What is an electrophile?
  • What is addition?
A
  • An electrophile is a lone pair acceptor
  • Addition: Reaction which increases number of substituents or convert double bond to single bonds or where two molecules from one molecule
34
Q

Explain why bromine, a non-polar molecule is able to react with propene

A
  • electron rich
  • Causes induced dipole in Br2
35
Q

Explain why bromine, a non-polar molecule is able to react with propene

A

• Bromine has temporary dipole-dipole interactions between its molecules
• Attracted to an area of high electron density

Organic Chemistry (13 decks)

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