Alkenes

Question 1

What is the general formula for alkanes

Answer 1

Cn H2n

Question 2

What type of hydrocarbons are alkenes

Answer 2

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

Question 3

Alkenes will generally have less what?

Answer 3

Hydrogens

Question 4

Why are C=C bonds unsaturated

Answer 4

Because they make more bonds with extra atoms in addition reactions

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Cyclic alkenes

Question 7

What type of addition reaction happens with alkenes?

Answer 7

Electrophilic addition reactions

Question 8

How do electrophilic addition reactions happen?

Answer 8

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

Question 9

Why do electrophilic addition reactions happen?

Answer 9

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

Question 10

What are electrophiles

Answer 10

Electron pair acceptors

Question 11

What charge do electrophiles carry and why?

Answer 11

Positive charge because they are short of electrons

Question 12

What is used to test for in saturation

Answer 12

Bromine water

Question 13

Describe the test for unsaturation

Answer 13

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

Question 14

Name two compounds Alkenes undergo Electrophilic addition with

Answer 14

• Hydrogen halides
• Sulphuric acid

Question 15

What is formed when alkenes react with hydrogen bromide?

Answer 15

Halogenoalkanes

Question 16

Adding hydrogen halides to unsymmetrical alkenes form what two products

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What are the three type of carbocations?

Answer 18

Primary, secondary and tertiary

Question 19

Draw the mechanism for the reaction of propene with hydrogen bromide

Answer 19

Check physical flashcards for answers

Question 20

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

Answer 20

• Cold concentrated sulphuric acid
• Alkyl hydrogen sulphates

Question 21

How are alkyl hydrogen sulfates formed into alcohols?

Answer 21

• 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

Question 22

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

Answer 22

Check physical flashcards for answers

Question 23

What is carbocation

Answer 23

An organic ion containing a positively charge carbon atom

Question 24

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

Answer 24

3-bromo-3-methylpentane

Question 25

Give the formula for percentage yield

Answer 25

Actual yield/Theoretical yield x100

Question 26

Give the formula for atom economy

Answer 26

Mass of useful product/total mass of product x 100

Question 27

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

Answer 27

• Yield: so you can use less starting material, reactants • Economy: So makes less (waste) product

Question 28

What areas are electrophiles attracted to?

Answer 28

electron rich areas

Question 29

When do addition reactions occur?

Answer 29

Where there is a double bond

Question 30

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

Answer 30

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

Question 31

What is the difference between addition polymerisation and condensation polymerisation

Answer 31

• 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

Question 32

Give the conditions needed to favour an elimination reaction

Answer 32

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

Question 33

- What is an electrophile? - What is addition?

Answer 33

- 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

Question 34

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

Answer 34

- electron rich - Causes induced dipole in Br2

Question 35

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

Answer 35

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