alkenes

What is stereoisomerism?

molecules with the same structural formula but different arrangement of atoms in a space

Q: State the feature of the C double bond that enables (named alkene) to exhibit EZ isomerism

They have restricted rotation about the planar carbon carbon double bond.

For an alkene to exhibit EZ isomerism what must happen

both carbons on the carbon carbon double bond must be bonded to 2 different atoms/groups of atoms

Q: Explain why but-1-energy doesn’t exhibit EZ isomerism

One of the C atom of the carbon carbon double bond is bonded to 2x H atoms.

pg5-6 identifying EZ isomerism examples

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Why are alkenes reactive?

due to the high electron density of the carbon carbon double bond

What is electrophilic addition?

the mechanism by which species (electrophiles) add across the double bond of alkenes

what is a electrophile?

electron pair acceptor

Q: Explain how alkene reacts with Br2 despite the br-br bond being non polar

Because the double bond is a high electron density area and induces a dipole in the br2

State reagent condition product and mechanism of halogen+alkene

r = halogen

c= room temp

p=dihalogenoalkane

mech =electrophilic addition

example of halogen+alkene mech on pg8

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State reagent condition product and mechanism of halide (H+Br,Cl,I etc…) +alkene

r - halide

c- room temp

p - halogenalkane

mech - electrophilic addition

State reagent condition product and mechanism of conc sulphuric acid+alkene

r - conc sulfuric acid

c - room temp

p - alkyl hydrogensulfate

mech - electrophilic addition

What is hydrolysis?

using water to break down covalent bonds

electrphilic mechanism example with conc acid on pg10

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State reagent condition product of how an alyklyhydrogensulfate makes conc sulphuric acid

through hydrolysis

r- water

c- warm

p - alcohol + sulfuric acid

alkene + water→

alcohol

sulfuric îs used up in step 1 electrophilic addition and regenerated in step 2 hydrolysis

Products of symmetrical alkene

1

Products of unsymmetrical alkenes

2

Products of unsymmetrical electrophiles

2

pg 11 major and minor product example

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Explain carbocation classification

tertiary carbocation - carbon with positive charge is attached to three carbon atoms

secondary carbocation - carbon with positive charge is attached to two carbon atoms

primary carbocation - carbon with positive charge is attached to one carbon atoms

Which carbocation is most stable?

tertiary

Q: Why 2 bromopropane is the major product?

it is formed via a secondary carbocation intermidiate. A secondary carbocation intermediate is more stable than a primary carbocation intermediate.

this is because the greater number of CH3 groups are more electron releasing and hence have a greater positive inductive effect

Q: Name the product formed when CH₃CHOSO₃HCH₂CH₃ is heated with water. Name the reaction

hydrolysis

butan2-ol

Name and outline the mechanism when concentrated sulfuric acid reacts with but-1-energy

Why is butan2hydrogensulfate the major product?

pg13

two products

major: butane 2 hydrogensulfate

Formed via a secondary carbocation intermediate which is more stable than a primary. This is because the greater number of CH3 groups are more electron releasing and have a greater positive inductive effect

Electrophilic addition with two products example pg 13-14

What is an addition reaction?

it increases the number of subtitutents attached to an atom as a double bond is being converted to a single bond

Type of reaction, reagent, condition and product of ethene to ethane

r - hydrogen 2

c - 150 degrees, nicely catalyst

reaction - addition

product - alkane

Type of reaction, reagent, condition and product of ethene to ethanol

reaction - hydration

r - water

c- concentrated phosphoric acid catalyst, 300degrees,60atm

p - alcohol

What is hydration?

the addition of water

product of addition reaction and hydration reaction

alkane

alcohol

Define acid

proton donor

Show the mechanism hydration of ethene pg 16 +examples

Role of H+ in hydration mechanism

catalyst - regenerated at the end of the reaction

Mechanism of alcohol to alkene

elimination

What is elimination? reagent and condition

an atom or group of atoms is removed from a reactant

r - conc sulfuric/phophoric acid

c - heat

example elimination pg 17 s

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experimental appartusto convert alcohol to an alkene using conc sulfuric acid pg18

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How does alkene vapour form why?

alcohol and alkene both have hydrogen bonds between molecules but alkene has vow forces between molecules

When 2,2 dimethylpropan-1-ol is heated with conc sulfuric acid no alkene is formed why?

diagram on pg18

the carbon bonded to the C-OH does not have any H’s attached to it

What is a polymerisation reaction?

many small molecules (monomers)join together to form a very large molecule called polymer with a high Mr

Q: What are the main differences between addition and condensation polymerisation?

a - one product formed (polymer). Only one monomer. Monomers are alkenes

c- two products (polymer+small molecule). Two monomers.

Exam questions pg 19 about polymers

What is the repeating unit?

a specific arrangement of atoms that occur in the structure over and over again

polymer examples pg20-21

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Q: Draw the intermediate formed when 2methylpropene is reacted with bromine. explain your answer

back page mech drawing carbocation (tertiary)

A tertiary carbocation is more stable than a primary carbocation intermediate

the 2x CH₃ groups are more electron releasing/have a greater positive inductive effect than 2x H’s