Topic 18 - Organic Chemistry: Arenes
What is a halogen carrier
- AlX3, FeX3 where X is a halogen and it is a catalyst for the halogenation of arenes. They produce strong + electrophile which is needed as benzene is stable
Explain the bromination of a benzene ( electrophilic substitution)
- Benzene and BR2 heated under reflux - with AlCL3, ALBR3 as halogen carriers - Bromobezene and HBR is formed
Explain the alkylation reaction
- Benzene reacts with alkyl group like CH3CL to make methylbenzene and HCL - Use ALCL3 as catalyst
Explain the combustion of benzene
- Burn with oxygen - water and CO2 formed - Smokey flame because carbon-to-hyrogen ratio - soot is formed - orange flame
Where can you find phenols naturally
- Crude oil
How did IR data contradict Kekules structure
- Cyclohexene has a peak of an isolated alkene c=c - however benzene has a peak which is typical of an aromatic C=C
Describe and explain the reactivity of bromine with cylcohezene and benzene
- Cyclohexene is electrophilic addition C6H10 + Br2 ---> C6H10Br2 - Benzene is electrophilic substitution C6H6 ----> C6H5Br + Br - using a halogen carrier - Benzene is more stable - electron density in benzene is lower
What are the two scientists that are associated with benzene + halogen carriers
- Frieda - Crafts
Where can you find benzene naturally
- In crude oil
Explain how x- ray diffraction contradicted Kekules structure
- It showed that the bond length in benzene are all the same - However C=C are shorter then C-c - Using X ray diffraction we see that the bond length is an intermediate between the length of the double and single bond
Why is the benzene have a higher boiling temp than ethanol
- London forces between benzene molecules are stronger than the hydrogen bonds between the ethanol molcules
Why does phenol solid at room temp and slightly soluble in water
- OH group is polar - it can take part in hydrogen bonding - phenol molecules attract each other strongly and so has a mp higher then room temp - it can also form hydrogen bonds with water
Explain the new correct model of benzene
- Pi bonds are formed by an overlap of P orbitals - each carbon has 1 electron in the P orbital - One large pi bond is formed with 6 electrons shared across the "cloud" - these are all delocalized -
What are some used for phenols
- TCP antiseptic - polymer
Explain why there are 3 isomers of Dibromobenzene and not 4
- This is because it showed that the bonds between all the carbon atoms are the same and not some c-c and others C=c
Explain the hydrogenation of benzene
- addition reaction - heat under pressure - nickel catalyst neeed - Circle leaves as all single bonds
Explain the acylation reaction
- benzene group react with acyl group like ethanoyl chloride to make a ketone (phenylethanone) and HCL - using ALCL3 catalyst -
What is TCP
- chlorination of phenol - it known as antiseptics
Explain the nitration of benzene
- electrophilic substation - NO2+ is the electrophile - react Conc nitric acid and sulfur acid to make No2+ H2SO4 + HNO3 ---> HS04- + H2NO3+ ( not stable ) H2NO3+ ----> NO2+ + H20 - This reaction is very exothermic so multiple NO2+ will react so they is why is should be cooler temp - Nitrobenzene and water formed
What happens when you react the Phenol with acyl chloride
- ester and HCL formed - if you react it with ethyl ethanoate you will make phenyl ethanoate )
Why should the nitration of benzene kept between 50-60
- if its to high dinitrobenzene or trinitrobenzene will form - if too low the reaction is to slow
How does phenol react differently with bromine then benzene and explain
- it delcolourses bromine and white ppt forms. at room temp with no catalyst - phenol is weaker because lone pair of electron sin p orbital of oxygen interacts with delocalized pi bonds in the ring - so electron density has increase through a process called activation because molecules now more reactive towards electrophile - br-br is polarized by benzene so Br+ formed - White ppt is 2,4,6 tripbromophenol as br2 reacts 3 times as the reaction happens more readily then benzene
What are some physics properties of benzene ( color, solubility, nature)
- it is colorless - insoluble in water - toxic and a carcinogen ( causes cancer)
Why phenol are more reactive then benzene with Br
- lone pair of electrons from the oxygen - increase the electron density on the ring - make It more susceptible to electrophilic attack
What do you name benzene ring with NH2
- phenyl amine
How can you test for phenol
- react with FeCL3 it will turn purple is phenol
Explain the sulfonation reaction
- replace H on benzene with -SO3H - React with fuming sulfuric acid ( dissolve SO3 with conc sulfuric acid ) - temp at 40 C - water and benzenesulfonic acid is made
Explain why Benzene doesn't decolouriose bromine water
- this is because it is more stable - all pie bonds are delocalised - It forms HBR and Bromobenzene with AlBR3/FeBR3
Why benzene molecule is planar?
- trigonal planar -bonded at 120 -joined by pi bonds
Why should conditions be anhydrous for the friedel-crafts reactions
- water will react with catalyst or sometimes the organic product
How did thermochemical data contradict Kekules structure
-Enthalpy change of hydrogenation theoretically is much larger more exothermic - this shows that the bonds are 'weaker then the c=c bonds ' - This is also because bond length is an intermediate length
Why all c-c bond sin benzene the same length
-pi electrons are delocalized - in resonance - electrons are evenly distributed
Mechanism of Bromination of Benzene
1: Formation of Electrophile AlBR3 + Br2------> Br+ AlBr4- 2: Electrophilic attack Curley arrow from circle to Br+ 3: Formation of aromatic product bromo bezene and H+ formed 4: regeneration of catalyst AlBr4- + H+ ------> AlBr3 + HB4
Mechanism for the alkylation of benzene
1: Formation of Electrophile AlCL3 + CH3Cl ---> CH3+ + AlCl4- 2: Electrophilic attack Curley arrow from circle to the electrophile 3: Formation of aromatic product Methyl benzene and H+ formed 4: regeneration of catalyst AlCl4- + H+ ----> AlCl3 + HCl
Mechanism for the acylation of benzene
1: Formation of Electrophile AlCl3 + CH3COCL ---> CH3CO+ + AlCL4- 2: Electrophilic attack Curley arrow from circle to the electrophile 3: Formation of aromatic product Phenylethanone formed and H+ 4: regeneration of catalyst AlCl4- + H+ -----> AlCl3 + HCL
Mechanism for Nitration of benzene
1: Formation of Electrophile HNO3+H2S04 ---->NO2+ +HSO4- + H20 OR HNO3+H2SO4---> HS04- + H2NO3+ H2NO3+ ----> NO2+ + H20 2: Electrophilic attack Curley arrow from ring to electrophile 3: Formation of aromatic product Nitrobenzene formed 4: regeneration of catalyst HS04- + H+ ----> H2SO4
What are the 5 problems with Kekules structure of benzene. Outline
1: it does not declourlise bromine water 2. There is 3 isomers if Dibromo benzene and not 4 3. X- ray diffraction shows bond length as intermediate 4. Thermochemical data shows enthalpy of hydrogenation is smaller 5.Infra red shows different absorption pattern
How many electron is sigma bonds in benzene
24 two in c-H Two in c-c
What is an arene
A compound that contains a benzene ring - Contains double bond one
What reagents and conditions do you need to convert benzene into chlorobenzene
AlCL3 + CL2
Write an equation to show the formation of the electrophile during the reaction between bromine and benzene.
Br2 + AlBr3 ----> Br+ AlBr4-
How many electrons in a pi bonding in benee
Each carbon supplies 1 so 6
Illustrate the initial role of sulfuric acid in this reaction
HNO3 + H2S04 -----> H2O + NO2+ + HSO4-
Suggest why the product of the reaction between bromine and benzene, bromobenzene, is still unsaturated.
The ring of pi electors in benzene is a stable configuration It is unchanged after the reaction
What is phenol ( weak, strong base/acid)
Weak acid
What is the essential property of sunscreen
absorbs UV
What happen when you react phenol with NaOh
acid + base ----> salt and water
What is NH2 functional group called
amine
What type of compound is benzene
aromatic
What type of reaction is propene and bromine
nucleophilic addition
How to convert a nitrobenzene into a phenyl amine
react with conc HCL and SN Heat under reflux
What happens to the Amine group when you react it with an acyl chloride
you get an amide
