• 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

• 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

• 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

• because the benzene ring is stable

• arene/ aryl compounds/ aromatic compounds

• C6H5CH3

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

• bromine with FeBr3 catalyst (iron filings + Br2) (anhydrous)
• chlorine + FeCl3 catalyst or AlCl3

• 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

• Boiling methylbenzene and chlorine gas under the presence of UV light
• temperature: 55 degrees/ 25-60 degrees

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

• methylbenzene is refluxed with alkaline potassium manganate (VII) 
• acidified with dilute sulfuric acid
• becomes benzoic acid.

• need to remember the reactions and conditions

• 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.

• 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

• Benzene + Br2/Cl2 with anhydrous AlCl3/AlBr3 catalyst

• Methylbenzene + AlCl3/AlBr3
• Electron donating: 2,4
• If the halogen is in excess: 2,4 or 2,6 or 2,4,6

• boiling methylbenzene and chlorine gas with UV light
• benzene does not undergo this
• in excess, all three hydrogen atoms in methyl will be substituted

• Benzene + no2
• HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+
• Nitrating mixture is refluxed at 55°C 
• Further nitration: 1,3 or 1,3,5

• benzene + halogen bonded alkyl group with AlCl3 catalyst

• benzene + R-C=O group with AlCl3 catalyst

• always gives benzoic acid

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

• 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

• 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.

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)

• 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)

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.

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

• 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

•  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

• Delocalised pi bonding electron will remain intact due to aromatic stabilisation
• High density around benzene ring attract electrophile

• new syllabus stated AlCl3/ AlBr3 instead of FeBr3 for the catalyst
• AlCl3 is called as halogen carriers 

• Br will have lone pair of electrons
• Forming of double bond

• 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.

• Aryl/aromatic compounds 
• C6H6
• Planar
• Perfectly symmetrical

• Chlorobenzene
• Nitrobenzene
• Toluene
• Phenol

• Electrophilic substitution
• Nitration
• Alkylation / Friedel - Craft Reaction
• Reaction of Phenol 

• 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 

• 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

1. Electrophilic Substitution 

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

• 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 

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

• 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

• 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

• C6H6
• planar
• perfectly symmetrical
• organic hydrocarbons with benzene rings are called arenes/aromatic compounds

• 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 

• + 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)

• stronger
• lone pair of halogen atom overlaps with pi bonding system in benzene ring
• gives partial double bond character

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

• “nitrating mixture” (conc. HNO3 + conc. H2SO4)
• refluxed at 55 degree (25-60 degrees in textbook)
• NO2+ electrophile 
• activates position 3 & 5

•  Formula:  C6H6
• Hexagonal shape with 6C atoms
• Perfectly symmetrical

• Delocalised pi bonding electron will remain( aromatic stabilisation)
• Initial attack is done by electrophile 

•  AlCl3/ AlBr3 catalyst
• AlCl3 is called as halogen carriers 

•  under presence of UV light
• Br2( g)/Cl2(g)

• made from nitrating mixture of con HNO3 and H2SO4 
• Condition: refluxed with benzene at 55 degree to make nitrobenzene

• 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.

• 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℃.

• 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

• reacted with concentrated HNO3 and concentrated H2SO4
• Refluxed at 55°c

• alkylation: with the alkyl chain
• Acylation: with the acyl group
• Both of them are electrophillic substitution

• oxidising agent: potassium manganate (VII)
• Refluxed & added H2SO4

• catalyst: nickel/ aluminum 
• Refluxed

•  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

• 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

• Reagent: dry Cl2 gas/ pure Br2 liquid
• Condition: rtp
• Catalyst: anhydrous AlCl3 solid / FeBr3 Solid

• Reagent: nitrating mixture , conc. HNO3/ H2SO4
• Condition: 45-55°C under reflux
• 
  

• 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

• 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 

• Halogenation
• Nitration
• Alkylation

1. the difference in bond lengths give a distorted hexagonal shape
2. benzene requires harsher conditions to undergo electrophilic addition

1. halogenation
2. nitration
3. alkylation / acylation

1. hydrogenation

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