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1.benzene(C6H6)
-planar
-sp2(doublebond)
Symmetrical
-pie bonds
-stable
2.electrophilic substitution
Benzene react with Cl2 or Br2 with the help of the AlCl3/FeCl3 as catalyst.condition must be in room temperature.Benzene attack by an electrophile which could be addition or substitution but benzene is too stable hence only substitution reaction can happen.
3.nitration of benzene
Hydrogen is replaced with the NO2 after reaction with Conc HNO3/H2SO4.condition 50 degree celcius.
4.friedel crafts reactions
Acylation reaction,the benzene become ketone after react with the alcyl chloride with catalyst ALCl3,reaction form acylium ion then attack the benzene in an electrophilic substitution.The hydrogen is replaced with the halogenoalkane and the hydrogen will react with Cl ion to horm HCl

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Benzene
- C6H6
- hexagonal
- carbon is sp2 hybridized + 3 sigma bonds

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Benzene
-formula of c6h6
-both symmetrical and planar
- It's an aromatic compound
-very emotionally stable

😍

-also learned that arenes are basically organic hydrocarbons with benzene rings

Rejection of old benzene structure

😔

-different lengths of carbon bond which caused the benzene structure to be not symmetrical

-benzene need harsher conditions to experience to get it going(electrophilic addition)

Reactions of Arene:
-Alcl3 or AlBr3 as catalysts
-undergoes electrophilic substitution

Bond strength of C-halogen
-halogenoarenes have stronger carbon halogen bonds than halogenoalkanes due to a lone pair in the halogen atom

Free radical substitution
-something benzene will never do due to methyl group

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Benzene (C6H6)
-has symmetrical hexagon shape, very stable (old structure rejected coz different bond lengths n conditions)
-undergo electrophilic substitution (where electrophile attacks pi bond, accepting a pair of electron from benzene. It forms a positive intermediate with delocalised electrons. proton is then eliminated and it stabilises)
-reaction with chlorine or bromine (Al/FeCl3, Al/FeBr3)
-nitration of benzene(refluxed at 55c, producing nitrobenzene, NO2+ electrophile)

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1.Benzene
C6H6
Planar
Symmetrical
Sp2
Reaction: Halogenation
-Iron/aluminum catalyst
-rtp
Reaction: nitration
Reflux 55C
Reaction: free radical
Reagent Cl2
UV light
No subs in ring benzene
Reaction: oxidation
Potassium magnate
Bond strength C-Halogen
Stronger
Give partial double bond character.

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Benzene
- a hexagonal shape made out of six carbons
- symmetrical
- Planar
- C6H6
- aromatic compound
Evidences to reject the old benzene structure
- there are three shorter carbon-carbon double bonds and three longer carbon-carbon single bonds therefore structure would be distorted
- requires harsher conditions to go through addition reaction
-Main mechanism for arena reactions is electrophilic substitution
- arenes: electrophilic substitution
- alkenes: electrophilic addition
- -OH group joined to a benzene ring will result to a compound called phenol
- methylbenzene or aklylarenes halogenated in position 2 or 4

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benzene
- C6H6
- hexagonal
- planar
- Friedrich August proposed that benzene was perfectly symmetrical
- evidences to reject old benzene structure:

1. the difference in bond lengths give a distorted hexagonal shape

2. benzene requires harsher conditions to undergo electrophilic addition

reactions of arenes
- electrophilic substitution

1. halogenation

2. nitration

3. alkylation / acylation

- free radical substitution
- oxidation
- electrophilic addition

1. hydrogenation

I need to familiarise myself better with the different reaction mechanisms and the conditions required for each reaction.

The teaching was at a good pace and Mr. Gopi continuously revises important points in this chapter, making it easier to follow and understand the different parts, especially the reaction mechanisms. The lecture was very compact with information as well, and the youtube videos are very useful as revision materials.

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From today's lecture, I learnt about

Structure of Benzene

- a hexagonal shape made of six carbon atoms (C6H6)

- organic hydrocarbons with benzene rings

arenes/ aryl compounds/aromatic compounds

- planar

- perfectly symmetrical

Two of the pieces of evidence for the rejected old benzene structure would be that

- since in Kekule's structure, the three carbon-carbon double bonds are shorter while the three carbon-carbon single bonds are longer; so the shape would've been a distorted hexagonal shape

- they require harsher conditions for addition reaction

In addition to that, it is important to note that each carbon in the hexagonal ring is sp2 hybridized and has 3 sigma bonds. I have also learnt how to name aryl compounds and the reaction of arenes which includes:

- Electrophilic Substitution

Halogenation

Nitration

Alkylation

- Free radical substitution
- Oxidation
- Electrophilic addition

It was a great lecture, and I really enjoy how Mr Gopi always does a recap at the start of each class, since this helps refresh our minds. Other than that, it was a clear and concise lecture. I think I need to revise more on the different reactions as there are quite a number of them.

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Benzene
- Hexagonal shape
- 6 Carbon atoms

Arenes
- Also known as aryl compounds or aromatic compounds
- Organic hydrocarbons with benzene rings (Ex : C6H6)
- Planar
- Perfectly symmetrical

Rejection of old benzene structure
Statement #1 : Kekule's structure is 3 shorter C=C bonds & 3 longer C-C bonds
Answer #1 : False
• It would be a distorted hexagonal shape
• Benzene requires harsher conditions to go through addition reaction. Each C atom is sp2 hybridized & contribute 1 electron to a π bond and delocalized over all C atoms in hexagonal ring

Electrophilic substitution
- Reaction with Br with FeBr3 catalyst
• FeBr3 is iron fillings
• Br molecule is polarized to form Br electrophile, which forms dative bond by donating lone pair of electrons to empty d iron orbital

- Reaction with Cl2 with FeCl3 or AlCl3 catalyst
• FeCl3 is iron fillings
• Halogen carriers

Halogenation
- Also known as Halogen Electrophile Substitution
- Halogens substituted in position 2 or 4 when methyl benzene or other alkylarenes are halogenated
- Activated by electron-donating groups bonded directly to benzene ring
- Mixture of compounds formed

C-halogen bond strength
- Stronger in halogenoarenes than halogenoalkanes
• One lone. Pair on halogen atom overlaps slightly with π bonding system of benzene ring
• Results in partial double bond character

Free Radical Substitution
- Between methylbenzene & Cl2 gas
- Boiling
- UC light
- No substitutions into benzene rings
- If in excess, all 3 H atoms in methyl is substituted

Electrophilic Substitution
- Nutrition of benzene
- NO2 introduced into molecule
- Reflux at 55C (25C - 60C)
- Forms nitrobenzene

Mechanism
- Stage 1 : Electrophile attracted to high density of π bonding in benzene
• Pair of electrons from benzene ring donated
• Forms covalent bond
• Delocalized ring is disrupted
• Result is 4 π bond electrons & (+) charge spread over 5C atoms

- Stage 2 : Restoration of full delocalized ring
• C-H bond broken heterolytically
• Both electrons go into π system
• Further nitration to produce 1,3-dinitrobenzene & 1,3,5-trinitrobenzene
• NO2 withdrawn to activate 3 or 5 positions

Alkylation
- Also known as Acylation
- Introduction of acyl group (Carbonyl C=O & Alkyl)
- Friedel-Crafts reaction
• Introduction of side chain into benzene ring
• Carbocation (electrophile carrying (+) charge on C atom) attacks benzene ring
• Add AlCl3 catalyst to halogenoalkane to form electrophile

Oxidation of side-chains
- Alkanes not typically oxidized by potassium manganate (VII)
- Alkane side-chain oxidized to form carboxylic acid in alkylarenes

Electrophilic Addition
- Also known as Hydrogenation
- Use H2 & Pt/Ni catalyst
- Heat
- High pressure

Improvements : Need to revise more
Lecture : Good

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Benzene:
- Hexagonal
-C6H6
-Arenes are organic hydrocarbons containing one or more benzene rings
-Aromatic compund
-Sp2 hybridised carbon atom
-Stabilisation energy is high-->very hard to break hence only undergoes substitution

Electrophilic subs with chlorine & bromine
-React with bromine with anhydrous FeBr3 catalyst
-React with chlorime gas bubbled through benzene at rtp with FeCl3 or AlCl3 catalyst. Products are cholorobenzene, hydrogen chloride/hydrogen bromide (depends on catalyst used)
-Substitution using UV light, side chain will be affected.
-Substitution using halogen carriers, the inside of the ring will be substituted

Nitration
-Refers to the introduction of NO2 group into the molecule.
-NO2+ ion which is the electrophile is made from mixture of concentrated HNO3 and concentrated H2SO4.
-Mixture is refluxed with benzene at around 55 C

Alkylation/Alcylation
-Subs hydrogen to the benzene ring from alkyl; methyl (-CH3) or ethyl (-C2H5)
-Acyl group: contains an alkyl group and carbonyl (C=O)
-Can use AlCl3 as catalyst

Oxidation
-Using potassium manganate (VII) as oxidising agent.

Hydrogenation
-Hydrogen gas, nickel/platinum catalyst.

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Benzene (C6H6)

6 carbon atoms with each atom holding one Hydrogen atom for a total of 6 hydrogen atoms in the ring

Has a hexagonal structure which includes 3 double bonds and is symmetrical

The 3 Doubles bonds separated by single bonds caused it to be knows as having pi bondings

Benzene is stable due to the fact that six electrons from the six carbon atoms become delocalized across the molecule

- Reactions

Halogenation: benzene reacting with chlorine in a presence of a catalysts with either iron (Fe) or aluminum (Al) as the catalyst. Condition of the reaction is that it must happen in room temperature, the reaction occurs for which the benzene is attacked by an electrophile which results in either the addition or substitution of hydrogen atoms since halogenation is an electrophilic substitution reaction.

Free radical substitution: an example of a free radical substitution with benzene is when benzene is in the form of methylbenzene in which its just a methyl group attached to the benzene ring, reaction takes place when methylbenzene and chlorine react in the presence of UV light, how this happens is that the hydrogen atoms in the methyl group will be replaced by the chlorine atom in a substitution reaction

Nitration: reaction takes place when hydrogen atoms around the benzene ring is replaced by NO2 after reacting with nitrates (nitric acid) in a temperature of around 50 degree Celsius where nitrobenzene is formed, concentrated sulfuric acid is used as a catalyst where 1,3 dinitrobenzene is formed.

Friedel crafts reaction: in this acylation reaction, the aromatic ring which is the benzene would become a ketone after benzene would react with an acyl chloride with the presence of a catalyst (AlCl3), this reaction would form an acylium ion which is RCO+ which then attacks the benzene in an eletrophillic reaction where a hydrogen atom replaced previously attaches itself to a chloride atom from the acyl chloride forming HCl, this is when acyl benzene is formed + HCl

Hydrogenation: this reaction will result in which hydrogen atoms are bonded forming a cycloalkane in which delocalised electrons from the benzene ring would be broken down since they bonded to hydrogen atoms, this happens in a temperature of 150 degree Celsius with high pressures

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Benzene is made up of 6 carbons in a hexagonal shape. They are planar,perfectly symmetrical and have the structure C6H6.

Benzene does not use the kekule’s structure as according to the structure there are 3 short carbon double bond and 3 long carbon single bond which means it is no longer symmetrical. Also Benzene requires harsher conditions to go through addition reaction.

In benzene, each carbon is sp2 hybridized and has 3 sigma bonds.

Phenyl groups are C6H5

Learnt about aromatic stabilisation and the bond strength of carbon halogen bonds in halogenoarenes. P.s. They do be stronger than in halogenoalkanes as one of the lone pairs on the halogen atom slightly overlaps with pi bonding system of benzene ring. Essentially they have partial double bond charactar.

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Benzene hexagonal C6H6

6 C-C single bonds

each carbon forms 3 sigma bonds ( 2 between carbon and carbon on either side, 1 between hydrogen and carbon)

perfectly symmetrical

classified as hydrocarbon

clear colorless liquid at rtp

Volatile and has low bp

Relatively unreactive ( strong bondings)

Burns with smoky flame

Electrophillic subsitution mechanism

An H-atom on the ring can be substituted by other atoms/groups

All carbon atoms identical and benzene ring symmetrical hence any H-atom can be substituted

E⁺ attacks π e⁻ ring, accepting a pair of e⁻ from benzene

An intermediate +ve specie is formed in which positive charge is delocalized around the ring (more stable than a normal carbocation)

Proton eliminated from positive intermediate to restore stability and π system of delocalized e⁻s reformed

Electrophilic substitution

Halogenation:

Reagent: dry Cl2 gas/ pure Br2 liquid

Condition: rtp

Catalyst: anhydrous AlCl3 solid / FeBr3 Solid

Nitration:

Reagent: nitrating mixture , conc. HNO3/ H2SO4

Condition: 45-55°C under reflux

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Formula: C6H6

A very stable aromatic compounds

Sp2 hybridization

Trigonal planar, 120°

Undergoes electrophillic substitution (most)

Reactions:
1. Halogenation:

iron/ aluminium catalysts

Electron-donating groups causes products halogens to be at position 2 or 4

The stronger the electron donating group, the more substituent can be placed in the benzene ring

2. Nitration:

reacted with concentrated HNO3 and concentrated H2SO4

Refluxed at 55°c

3. Friedel-crafts

alkylation: with the alkyl chain

Acylation: with the acyl group

Both of them are electrophillic substitution

4. Oxidation

oxidising agent: potassium manganate (VII)

Refluxed & added H2SO4

5. Hydrogenatiom

catalyst: nickel/ aluminum

Refluxed

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arenes undergo electrophilic sibstitution

arenes do not undergo addition because its double bonds would be broken and the delocalization and it will loose stability

in elctrophilic substitution with Cl, the Cl+ cation will move to the catalyst AlCl3 and the other Cl+ cation will attach to the benzene

if use UV light as catalyst methyl side chain is not affected and can attach to Cl+ making CH2Cl attacj to benzene

NH2,NHR,NR2,OH,OR attack the 2,4,6 position of benzene

NO2,N+H3,CN attack the 3,5 positions

alkylation or acylation of benzene (friedel-crafts reaction) is another example of ectrophilic substitution

alkylbenzene will always be oxidised to form benzoix acid

phenol is a weak acid

OH group in phenol enhances the reactivitu of benzene

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Benzene - hexagon made of 6 carbon atoms (C6H6)
arenes / aryl compounds - organic hydrocarbons with benzene rings
Benzene : planar & perfectly symmetrical molecule
Evidence that limits Kekule’s -
1. C=C shorter than C-C, hence distorted hexagonal shape
2. C-C supposed to undergo addition, but Benzene requires harsher conditions

Reactions
1. Electrophilic substitution
reagent : Cl2/Br2
catalyst : anhydrous Al3 / FeBr3 (halogen carriers)
condition : rtp
C6H6 + Br2 —> C6H5Br + HBr

2. Halogenation
catalyst : AlCl3
• Methylbenzene/alkylarenes halogenated, halogens substituted in position 2 & 4
• Positions activated by any electron donating groups bonded directly to benzene ring
• Mixture of compounds formed

3. Free Radical Substitution
• Benzene does not undergo substitution
• methylbenzene undergo as there is H not directly bonded to benzene ring
• boiling required

C6H5CH3 + Cl2 —> C6H5CH2Cl + HCl

reagent : Cl2
Condition : UV light

4. Nitration (electrophilic substitution)
electrophile : No2+
HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+
reagent : conc. HNO3 + H2SO4
Condition : reflux at 55°C (25°C - 60°C)
C6H6 + HNO3 —> C6H5NO2 + H2O
further nitration produces 1,3-dinitrobenzene & 1,3,5-trinitrobenzene as NO2 is electron withdrawing and activates 3 or 5 positions

5. Alkylation / Friedel-crafts reaction
• substitute CH3 and C2H5
• introduce alcyl group

Reagent : alkyl halide / acyl chloride
Condition : heat under reflux
Catalyst : anhydrous AlCl3

6. Oxidation
• reflux with alkaline KMnO4/K2Cr2O7
• acidified with dilute H2SO4
• no matter the alkyl chain, product is always benzoic acid, extra carbon lost as CO2
Test for alkylbenzene & akkane : reflux with alkaline KMnO4 (purple —> colourless)

7. Hydrogenation (electrophilic addition)
• aromatic stabilisation
Catalyst : Pt/Ni
Condition : heat & high pressure (150°C)

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Benzene Structure:

C₆H₆ with hexagonal structure

Has a ℼ bonding system (in the form of a ring of delocalised electrons above and below the carbon atoms)  made by the overlap of p orbitals.

This is why benzene has a C-C bond length longer than C-C and but shorter than C=C making it have a symmetrical shape.

The ℼ bonding system is also why benzene is very stable, causing addition reactions to require harsher conditions than substitution reactions. (aromatic stabilisation)

In Halogenoarene: slight overlap between a lone pair in the halogen and the ℼ bonding system of the benzene, giving the bond a partial double bond character.

Reactions of Arenes:

High density of electrons makes the reactions electrophilic.

Substitution with Halogen: require halogen carriers (AlX₃ or FeX₃) to form the electrophiles when dative bonding occurs between the polarised halogen molecule and the halogen carrier.

Electron-donating groups like NH₂, OH, alkyls and halogens activate the benzene ring at positions 2 & 4.

Free radical substitution of side chains: when boiled and in the presence of UV light, the H atoms in the side chains will be substituted by the halogen gas but not the H atoms in the benzene ring itself.

Nitration: require conc. nitric acid and conc. sulfuric acid to form NO₂⁺ (HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄ + H₃O⁺), and then refluxed at 55℃.

Electron-withdrawing groups like NO₂, COOH activate the benzene ring at positions 3 & 5.

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Benzene

Characteristic:

Formula:  C6H6

Hexagonal shape with 6C atoms

Perfectly symmetrical

Structure:

The old one is rejected because will not form a perfect symmetrical and electrophilic addition process will be too easy when benzene is really stable and requires harsher condition.

Arenes

Delocalised pi bonding electron will remain( aromatic stabilisation)

Initial attack is done by electrophile

Electrophilic substitution

AlCl3/ AlBr3 catalyst

AlCl3 is called as halogen carriers

Free Radical Substitution

under presence of UV light

Br2( g)/Cl2(g)

Nitration of Benzene

made from nitrating mixture of con HNO3 and H2SO4

Condition: refluxed with benzene at 55 degree to make nitrobenzene

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Benzene:
C6H6
Symmetrical hexagon shape
Reactions are halogenation, free radical substitution, nitration, friedel-craft’s reaction, oxidation, hydrogenation

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Benzene:

C6H6

planar

perfectly symmetrical

organic hydrocarbons with benzene rings are called arenes/aromatic compounds

Why old structure is proven to be not accurate?

carbon bond lengths are not the same ( distorted shape, carbon bond of benzene is between both single bond and double bond)

To experience electrophilic addition, harsh conditions are needed for benzene

Aromatic stabilization (benzene ring stabilize benzene structure)

each carbon ring is sp2 hybridized

Reaction of Arene (electrophilic subs):

+ Br2, with anhydrous AlBr3/FeBr3 catalyst

or + Cl2, with anhydrous AlCl3/FeCl3 (halogen carriers)

halogen atom substitutes into benzene ring at position 2 & 4, activated by electron-donating groups bonded directly to benzene ring

excess cl = can substitute at positions (2,4), (2,6), (2,4,6)

Bond strength of C-halogen in Halogenoarenes:

stronger

lone pair of halogen atom overlaps with pi bonding system in benzene ring

gives partial double bond character

Free Radical Subs:

Not possible with benzene ring as it doesn’t have methyl group

Nitration of Benzene:

“nitrating mixture” (conc. HNO3 + conc. H2SO4)

refluxed at 55 degree (25-60 degrees in textbook)

NO2+ electrophile

activates position 3 & 5

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Benzene

Hexagonal Shape made of 6 carbon atoms (C6H6)

Classified as a hydrocarbon

Arenes/Aromatic Compounds are organic molecules with benzene rings

Each carbon atom contributes its one spare electron to pi bond, delocalized over 6 carbon atoms

Very stable aromatic compound

Rejection of old benzene structure

Single bonded Carbons are longer than double bonded carbons, if   the old structure is true, benzene will not be perfectly symmetrical

Benzene undergoes substitution reaction, not addition reaction

Reaction of Benzene

1. Electrophilic Substitution

Reacts with Br2 in the presence of FeBr3 Catalyst  or Cl2 in the presence of FeCl3/AlCl3 Catalyst

Steps:

AlBr3 molecule polarizes a Br molecule

Bromine forms dative bond with AlBr3 by donating lone pair of electrons

Br2 becomes partially positive, creating electrophile (Br+)

Br+ cation an benzene ring become attracted to each other

2. Halogenation

Halogen atom substitute into benzene rings of Alkylarenes or methylbenzene at position 2 or 4

* Bond Strength of C-Halogen

Carbon-halogen bond is stronger in halogenoarenes than halogenoalkane, therefore halogenoarenes is less reactive

Reason: One lone pair on the halogen atom overlaps with pi bonding in benzene ring

3. Nitration

NO2 is introduced into molecule using NO2+ion as an electrophile

HNO3 + 2H2SO4 => NO2+ +2HSO4- +H3O+

Mixture is then refluxed with benzene at 55 degrees celsius

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Benzene:

Aryl/aromatic compounds

C6H6

Planar

Perfectly symmetrical

Types of Benzene:

Chlorobenzene

Nitrobenzene

Toluene

Phenol

Reactions of Benzene:

Electrophilic substitution

Nitration

Alkylation / Friedel - Craft Reaction

Reaction of Phenol

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Benzene

Simplest formula :  C6H6

Planar

Perfectly symmetrical

Old benzene structure is rejected because:

1. Won’t be perfectly symmetrical

2. Will undergo electrophilic addition way too easily, but benzene requires harsher condition

Reaction of arenes

Delocalised pi bonding electron will remain intact due to aromatic stabilisation

High density around benzene ring attract electrophile

Electrophilic substitution

new syllabus stated AlCl3/ AlBr3 instead of FeBr3 for the catalyst

AlCl3 is called as halogen carriers

Bond strength of C Halogen

Br will have lone pair of electrons

Forming of double bond

Free Radical Substitution

condition: under presence of UV light

Use Br2( g)/Cl2(g)

Doesn’t reauire halogen carriers so that gases won’t transfer to another place.

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I learned about:
- Benzene and its different compounds
- The structure of benzene rings
- The different names of all the benzene compound with a functional group
- Most reaction of benzene is electrophilic substitution
-electron-donating group usually gets into position 2,4,6
-electron-withdrawing group usually gets into position 3,5
- The mechanism of electrophilic substitution for benzene compounds

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Learn about :
* Benzene (C6H6, hexagonal shape, made of 6 carbon atoms, planar, perfectly symmetrical)
* Evidences to reject old benzene structure (kekule's structure) Different bond lengths
* Aromatic stabilisation (Benzene requires harsher conditions for addition reaction)
* Electrophilic substitution (AlBr3 catalyst)
* Electron donating (activates 2,4 positions)
* Bond strength of c-halogen in halogenarenes
* Free radical substitution (boiling under UV light)
* Nitration of benzene (conc. HNO3, H2SO4) (refluxed at 55°)
* Electron withdrawing (activates 3,5 positions)
* Hydrogenation of benzene ring (electrophilic addition) (Pt/Ni catalyst)

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BENZENE C6H6

- Benzene ring: hexagon made of six carbon atoms
- Found in medicine, dyes and plastics
- Organic hydrocarbons with benzene rings are called arenes/ aryl compounds/ aromatic compounds
- analytical techniques developed
- Found that benzene is planar
- Benzene requires harsher conditions to go through addition reaction. Example: catalyst, higher temperature, higher pressure
- Each carbon atoms contribute one electron to a pi bond and delocalized over all the six carbon atoms in the hexagon.

Reaction of arenes
- arenes are compounds that has benzene
- The delocalized pi bonding electrons remain intact for most reactions
- The initial attack is done by electrophile, which is attached to the high density around the benzene ring.
- Benzene + Br2 is electrophilic substitution. catalyst: FeBr3

Methylbenzene
- Alkyl or ch3 are electron donating group
- Amine, chlorine are also electron donation group
- Electro withdrawing group attack different position
- Carbon Cl bond is harder to break compared to carbon h because chlorine has 7 lone pair of electron. Lone pair of electron overlap slightly with the delocalized electron circle in the middle of benzene.
- Can undergo electrophilic substitution and free radical substitution
- Methylbenzene can undergo free radical substitution because the carbon is not attached to the benzene directly
- Methylbenzene will react with chlorine with the presence of uv rays
- Must be boiling methylbenzene
- NO2 is the electron withdrawing group

Nitration of benzene
- NO2 ion made form concentration nitric acid or concentrated sulfuric acid
- Nitrating mixture is refluxed with benzene at 55 degree Celsius to make nitrobenzene.
- Stage 1 the electrophile is attracted to the high density of the pi bonding of the benzene
- Stage 2 full delocalised ring is restored

Halogenation of benzene
- one of the lone pairs of the halogen atom overlaps slightly with the pi bonding system and make it stronger.

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benzene (C6H6) :

• hexagonal shape

• organic hydrocarbons with benzene rings are called arenes/ acrylic compounds/ aromatic compounds

(based on Friedrich August)

• planar

• perfectly symmetrical

• used to be in order to get C6H6, putting the three double bonds is required

• why prove false:

1. Carbon bond lengths are not the same

* carbon single bond is longer than carbon double bond

So it is a distorted shape not perfectly symmetrical

Later found out that carbon bond in benzene is between both

2. Alkene undergo electrophilic addition reaction because of carbon - carbon double bond

If there are three double bonds, electrophilic addition will happen easily but benzene requires harsher condition (higher temp and pressure)

* benzene ring will stabilise the benzene structure -> also called aromatic stabilisation

carbon is sp2 hybridised

carbon atoms for 3 sigma bonds

Electrophilic Substitution

• AlBr3 catalyst <- in current syllabus

• replace H with Br (if react with bromine)

• anhydrous <- without presence of water

• AlCl3 and Albrighton are also called halogen carriers

Halogen Electrophilic Substitution

• alkyl groups are donate electron

• activate position 2 and 4 when electron donating

• activated by electron donating groups

(examples: phenols and phenylamine)

• when there's excess chlorine, there will be more mixture of compounds

Bond strength of C Halogen in Halogenarenes

• the Br will have lone pair of electrons and will enter or overlap with the pi bond/ benzene ring

• there will be something like a double bond

Free Radical Substitution

• benzene does not undergo it as methyl group is absent

• Br2 gas and Cl2 gas can both be used

• under oresence of uv light

• Halogen carriers or catalysts are absent so Br or Cl will not go at other positions so the free radical substitution will focus more on the side chain

Nitrates of Benzene

• basically affine the NO2 group

• elctrophile is NO2+ ion (also know as nitronium ion or nitryl cation)

• 25 to 60 degrees Celsius <- in syllabus

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Benzene:

hexagonal, C6H6 molecule

Organic molecule with Benzene rings are called arenes/ aromatic compounds

Perfectly symmetrical

Each carbon atom contributes one electron to a pi bond and they’re delocalized all over the 6 carbon atoms.

Reasons  why the old structure is rejected

1. Bond length of C-C and C=C are of different lengths.

2. Benzene requires harsh conditions to go through electrophilic addition (aromatic stabilization)

Reactions of Arene

the delocalized pi electron remain intact for most reaction (aromatic stabilization)

Attacked by electrophile as high electron density around benzene ring

Electrophilic substitution

react with bromine/chlorine in the presence of AlBr3/FeBr3(bromine) and AlCl3/FeCl3 (chlorine)

Steps:

1. (Cl2/Br2) is polarized by the catalysts to form electrophiles (Br+/Cl+). This is done when Br2/Cl2 form dative bond by donating lone pair of e to empty d orbital of iron/aluminum.

2. Br+/Cl+ is attracted to e rich benzene

When alkylarenes are halogenated, halogens are substituted on positions 2&4 as these points are activated by the electron donating groups (phenol or phenylamine) bonded to benzene ring.

Strength of C-halogen in benzene

stronger than other organic compounds as the lone pair overlap with pi bond of benzene ring (giving a partial double bond character)

Nitration of benzene

introduction of NO2 into molecule using electrophile NO2+ (made from HNO3 + 2H2SO4 -> NO2+ +2HSO4- +H3O+)

Refluxed with benzene at 55 Celsius to make nitrobenzene

NO2 is electron withdrawing group, thus it activate position 3&5

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I learned about the structure of benzene, and why the current structure is accurate when compared with the older one. I also learned about the reactions it can undergo and the mechanism of these reactions.

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Oxidation of aromatic alkanes with KMnO4 to give carboxylic acids - Master Organic Chemistry

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Description: Treatment of an alkylbenzene with potassium permanganate results in oxidation to give the benzoic acid. Notes: The position directly adjacent to an aromatic group is called

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Learn about:

structure of benzene (planar, perfectly symmetrical)

kekule’s structure and why it’s not accurate

naming aryl compounds

Reaction of benzene: electrophilic substitution (halogenation, nitration), free radical substitution

electron donating group push into position 2,4,6 while electron withdrawing group push into position 3,5

mechanism for electrophilic substitution and free radical substitution

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Benzene

C6H6

hexagonal shape

planar, symmetrical

arenes are organic hydrocarbons with benzene rings

evidence that kekule's structure is not accurate: the bond lengths do not match with the C-C and C=C bond length

benzene requires harsher conditions for addition reaction (aromatic stabilisation)

high density around benzene ring attracts electrophile

Electrophilic substitution

Benzene + Br2/Cl2 with anhydrous AlCl3/AlBr3 catalyst

Halogenation

Methylbenzene + AlCl3/AlBr3

Electron donating: 2,4

If the halogen is in excess: 2,4 or 2,6 or 2,4,6

The carbon-halogen bond is stronger, because lone pair of electrons in the halogen atom overlaps slightly with the benzene ring, and will give a partial double bond character which is hard to break down.

Free radical substitution

boiling methylbenzene and chlorine gas with UV light

benzene does not undergo this

in excess, all three hydrogen atoms in methyl will be substituted

Nitration of benzene

Benzene + no2

HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+

Nitrating mixture is refluxed at 55°C

Further nitration: 1,3 or 1,3,5

Alkylation

benzene + halogen bonded alkyl group with AlCl3 catalyst

Acylation

benzene + R-C=O group with AlCl3 catalyst

Oxidation of side-chain in arenes

always gives benzoic acid

Hydrogenation (electrophilic addition)

Benzene + H2 and Pt/Ni catalyst with heat and high pressure

Produces cyclohexane

I need to revise more on memorising the different equations and conditions. The lecture was clear and understandable.

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Today i learned about benzene which is C6H6 and its compounds. The names of different benzene rings with functional groups such as nitrobenzene,phenol,and phenyl. I also learned that most of the reactions are electrophillic substitution and their reactions. Carbon double bond is much shorter and stronger than a regular double bond

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Learnt:
Traits of benzene
- Symmetrical
- Planar
- Electron ring and how it works

Reactions of Benzene

Substitution with Halogens
- Catalyst: AlCl3 / FeBr3
- Reactant: Benzene compound + Halogen

Substitution with NO2
- Condition: 55 C
- Reactant: HNO3 + 2H2SO4 (all conc.)
Reaction can also further proceed and replace more H with NO2

Substitution with Alkyls
- Catalyst: AlCl3
- Reactant: Alkyl with halogen bonded to it

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what i learnt:

benzene:

made up of 6 carbon atoms, hexagon shape, planar (2d molecule)

C6H6

has perfectly symmetrical molecule

there are 3 shorter carbon carbon double bond than 3 longer carbon carbon double bond

has 3 sigma bonds in each carbon

hybridization: sp2

has total of 6 electrons

needs a catalyst because it is stable

catalyst are halogen carriers

Why benzene dont go through electrophilic addition?

because the benzene ring is stable

organic hydrocarbons with benzene rings are called:

arene/ aryl compounds/ aromatic compounds

methyl benzene:

C6H5CH3

reaction of arenes:

Initial attack is done by electrophile, which is attracted to the high density around the benzene ring

Electrophilic Subtitution

bromine with FeBr3 catalyst (iron filings + Br2) (anhydrous)

chlorine + FeCl3 catalyst or AlCl3

Halogenation:

methylbenzene are halogenated

the halogens are substituted in position 2 or 4

One of the lone pairs on the halogen atom overlaps slightly with the pi bonding system of the benzene ring

Free Radical Substitution:

Boiling methylbenzene and chlorine gas under the presence of UV light

temperature: 55 degrees/ 25-60 degrees

Acylation:

attack on the benzene ring by an electrophile carrying a positive charge on a carbon atom

Oxidation:

methylbenzene is refluxed with alkaline potassium manganate (VII)

acidified with dilute sulfuric acid

becomes benzoic acid.

What i need to review more on:

need to remember the reactions and conditions

Comments on the lecture:

the lecture itself is detailed however sometimes it could be too fast but mr gopi always records the lecture so no problem because i could always go back and watch if i missed some things. he has also discussed with us the topic before the lecture so i could already understand some parts and not be blank when he is discussing the lecture.

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Learnt :
- benzene’s structure :
1. Planar
2. Hexagonal
3. Perfectly symmetrical
- double bond is relatively shorter than single bond
- each carbon is connected to 3 atoms and is sp2 hybridised
- naming aryl compounds ( varies ) :
1. Phenylamine
2. Chlorobenzene
3. Nitrobenzene
4. Phenol
- electrophilic substitution, its mechanism and conditions :
1. Halogenation
2. Nitration of benzene
- free radical substitution

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Benzene is a planar, symmetrical molecule with a hexagonal shape. It has a delocalised ring of electrons, giving it aromatic stabilisation!

It was originally mistaken to have 3 carbon-carbon bonds, and 3 carbon carbon double bonds. However, this was proven false after analysis showed that harsher conditions were required for it to undergo oxidation, and that its bond length is longer than a carbon-carbon double bond, but shorter than a carbon-carbon single bond. Its carbons are sp2 hybridized

ELECTROPHILIC SUBSTITUTION INCLUDED:
- Halogenation:
- Nitration:  Conc. H2SO4, Conc. HNO3, at 55 degrees.
- Alkylation
- Alcylation
All of these require halogen carriers // Catalysts! The mechanics are the same for all of them:
1. Catalyst polarises the reactant (etc. Cl2, Br2,)
2. Benzene ring is attacked by the newly formed electrophile (but the curly arrow must be drawn from the benzene, and towards the reactant)
3. Delocalised ring breaks and becomes positive, as a carbon atom is currently bonded to 2 other carbon atoms, H atom, and the electrophile. (2 electrons positive! as two electrons are needed to form the bond with the electrophile)
4. The C-H bond breaks heterolytically. The two electrons go back into the benzene ring, makes it stable again.
5. The H bond reacts to the halogen carrier/catalyst, regenerates the catalyst!

*excess would-be electrophiles is needed for further electrophilic substitution.

Electron donating (OH, -R which are alkanes btw, and -NH2): further substitution at 2,4,6
Electron withdrawing (NO2): further substitution at 3,5

Carbon-halogenation has a slight double bond character, as halogen p orbitals overlap with the depolarised ring ! Requires harsher conditions.

FREE RADICAL SUBSTITUTION:
- boil and UV ray light
if done to methylbenzene, 'Cl's will substitute the H atoms in the CH3 group. Nothing will actually be substituted into the benzene ring!

ELECTROPHILIC ADDITION IN HYDROGENATION:
- electrophilic addition
- uses Pt / Ni catalyst
- heat + high pressure
- creates cyclohexane
Cyclohexane will be formed! 3H2 is needed

OXIDATION:
no matter what the alkylbenzene is, it will be oxidised into benzoic acid! Water and/or CO2 produced!
Refluxed with alkaline potassium manganate(VII), and then acidified with dilute sulfuric acid.

hm the areas i need to study more are definitely the conditions for reactions! Especially for hydrogenation,,, I do believe i need to practise remembering and drawing acylation, the C=O bonds trip me up. I also dk why benzoic acid is formed every time???

I like the recap Mr. Gopi does before every lecture, I play mental catch up with it so i can check my own understanding from the lecture the day before. please keep doing it sir :D

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today learnt about benzene which is C6H6 and its structure(which is planar and symmetrical) as well as that arenes have rings of them. arenes also undergo several reactions which include halogenation, electrophilic substitution, free radical sub, nitration and alkylation and oxidation. need to study more on the reactions details and memorize (maybe make a sequence of letters or chart of similarities)

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Benzene: C6H6

Planar (2D): Each carbon atom in a trigonal planar (120 degrees)

Hexagon with a circle in the middle (electron ring consisting of 6 delocalised electrons, meaning that they are free to move above and below, like in metallic bonding and in C=C)

Each carbon has 3 sigma bonds

Each carbon is sp2 hybridised

Special case: delocalised electrons  in benzene can move around, while those in C=C have restricted movement

Evidence that Kekule’s structure is not accurate: bond lengths do not match C-C and C=C bond length, and it requires harsher conditions to undergo electrophilic addition

Alkane + Br2 (free radical substitution)

Alkene + Br2 (electrophilic addition)

Carbonyl + HCN (nucleophilic addition)

Arenes + Br2 (electrophilic substitution)

ES (halogen, NO2): Catalyst is needed for electrophilic substitution as benzene is stable: FeBr3, FeCl3, AlCl3, AlBr3. 2e- used for bonding with Br+ and e- ring disrupted, returned through heterolytic fission of C-H bond.

Electron donating: 2, 4, 6

Electron withdrawing: 3, 5

FRS: boil the arene and add Cl2 under UV

FCR: Introduction of a side chain by electrophilic attack using a halogenated compound, under heat.

Oxidation of SC: Refluxed with alkaline potassium manganate(VII), and then acidified with dilute sulfuric acid. Produces benzoic acid (only) and water and/or CO2.

EA (Hydrogenation): Addition of H2 with Pt/Ni catalyst, under heat and high pressure, produces cyclohexane.

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benzene
- hexagonal shape (C6H6)
- arenes are organic hydrocarbons with benzene rings
- planar
- requires harsher conditions for addition reaction (aromatic stabilisation)

reaction of arenes
- initial attack done by electrophile (attracted to high density around the ring)

electrophilic substitution
- use AlCl3 or AlBr3 catalyst

halogenation
- methylbenzene reacts with halogens, substituted in position 2 or 4
- if excess halogen, it is substituted in positions 2 and 4 or 2 and 6 or 2, 4 and 6

- lone pair of electrons in halogen will overlap slightly with benzene ring to form a partial double bond

free radical substitution
- requires boiling methylbenzene and UV light
- in excess, all three hydrogens in methyl is substituted nitration of benzene
- NO2+ electrophile made from conc. H2SO4 + HNO3
- refluxed at 55°C
- further nitration, NO2 will be at position 1, 3 or position 1, 3 and 5

alkylation - activates position 2, 4 and 6
acylation - benzene + acyl group (R-C=O)

oxidation
- gives benzoic acid (COOH)
- methylbenzene refluxed with alkaline K2MnO4 before it is acidified with dilute H2SO4

hydrogenation
- electrophilic addition
- uses Pt / Ni catalyst
- heat + high pressure
- creates cyclohexane

I need to fully memorise the reactions and their condition and do past paper questions to know what to expect for the exam. The teaching was clear and easy to follow.

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Today I learned about the structures of Benzene, which is both planar and symmetrical in shape as well. It also undergoes Electrophilic substitution, Halogenation, Nitration and Alkylation. Each of the reactions have different conditions.

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Benzene is planar, symmetrical and needs harsher conditions to undergo nucleophillic addition. This means it does not have three double bond like Kekule proposed.

Benzene undergoes electrophillic substitution:
> halogenation: needs FeBr3 or AlCl3 or FeCl3
> nitration: needs HNO3 + H2SO4 at 25C-60C
> alkylation: addition of an acyl or alkyl group needs AlCl3 catalyst

oxidation of the side chain in arenes produces a 1 carbon carboxyl group (excess carbon becomes CO2)

hydrogenation (electrophillic addition)
needs Pt or Ni catalyst
benzene + 3hydrogen -> cyclohexane

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1. Halogenation ( Electronic Subs )
2. Free Radical Substitution ( Not so applicable for Benzene )
3. Nitration ( Electronic Subs )
4. Friedel Craft's Reaction ( Electronic Subs )
5. Oxidation
6. Hydrogenation ( Need Pt or Ni Catalyst, High Temp and Pressure, forms Cyclic Alkane, Electronic Subs )
7. A lot of different reactions of Benzene
8. Benzene Structure: Planar & Symmetrical
9. Electronic Subs: Nitration

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Recalled:

Benzene structure:

thought to be planar and perfectly symmetrical

discovery of Kekulé's (though historians argue it was stolen from Archibald Couper and Josef Loschmidt):

Three shorter C=C bonds

Three longer C-C bonds,

hence distorted

Learned:

Electrophilic substitution:

Nitration requires concentrated sulfuric acid, concentrated nitric acid and for the reaction to be carried out in a temperature of 55°C

Friedel-Craft's reaction has two types: acyclation and alkylation of aromatix rings

Halogenation

Free-radical substitution isn't applicable to benzene

Oxidation

Hydrogenation involves electrophilic addition and requires a Pt or Ni catalyst and for the reaction to be carried out under high temperature and pressure

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In today's lecture, I learnt about:

- 2 evidence to reject the old benzene structure
- Naming aryl compounds
- Electrophilic substitution of arenes
• Nitration (55 degrees)
• Halogenation
• Alkylation
- Free radical subsitution (not available for benzene)
- Oxidation of the side-chain in arenes
- Electrophilic addition
•Hydrogenation (Pt/Ni Catalyst, harsher condition)
- The mechanisms and conditions
- Ring positions of substituent groups

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Today I learnt:
- The different reactions of benzene
- When benzene is reacted with excess halogen, it forms
- The mechanism of electrophilic substitution in halogenation, nitration, alkylation, and acylation.
- The conditions in nitration : Conc. H2SO4, Conc. HNO3, at 55 degrees.
- Further nitration causes the formation of
- Free radcial subsitution is not applicable for benzene.
- When ethylbenzene is oxidized, it still forms benzoic acid, and the other carbon is formed into CO2.
- Conditions for hydrogenation : Pt/ Ni
- Catalyst and high temperature and pressure.
- Hydrogenation forms a cyclic alkane
- Hydrogenation is electrophilic addition.