Benzene
Compound with benzene=aryl/ aromatic
Hydrocarbon=arene
Bonds
1. sp2 hybridization
3 σ bonds
2. Overlap of p orbitals
Rings of delocalized π bonding electrons
Reactions
Tend to maintain the stable π bond rings
Benzene= electron-rich nucleophile
1. Electrophilic substitution
1. Halogenation
==Electrophile=X+
Br2/ Cl2 in the presence of halogen carriers
e.g. AlBr3/ AlCl3
Electron-donating Alkyl group
For alkylarenes, position 2,4 are activated
C-X bond is stronger
Lone pairs in X slightly overlap with π bonding systems
Partial double bond character
Halogenoarene-->much less reactive
Not undergo hydrolysis
Presence of UV light-->free radical
With no substitution into benzene
2. Nitration
==Electrophile=NO2+
HNO3 + 2H2SO4 → NO2+ + 2HSO4− + H3O+
1. Benzene donate a pair to nitrogen
A positive charge spread across 5 carbon
2. C-H bond break heterolytically
Hydrogen leave as H+
3. Friedel-Crafts reaction
Electrophile=carbocation
Formed by adding AlCl3 catalyst to
1. halogenoalkane
2. acyl chloride
1. Alkylation
2. Acylation
Activating and deactivating groups
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1. Activating group (EDG)
Donating effect> withdrawing
or electron density via inductive effect
-NH2,-OH,-R
Resonance
Negative charge on ortho and para carbon
==Ortho/para director
Where electrophilic group-->more stable
2. Deactivating group (EWG)
Withdrawing> donating -->directing effect
-NO2,-CN,-COOH,-X
Resonance
Positive charge on ortho/para carbon
==Meta director
2. Oxidation of side chain
-CH3--> -COOH
1. reflux with alkaline potassium manganate(VII)
2. acidify with dilute sulfuric acid
3. Hydrogenation
Heat with H2, Pt/Ni catalyst
Forming cycloalkane
Phenol
High b.p. for arene
H bond
Preparation
1. NaNO2 + HCl -->HNO2+ NaCl
2. Add the phenylamine to Nitric(III) acid
3. Diazonium salt decompose in water
Acidity
C6H5OH(aq) ⇌ C6H5O−(aq) + H+(aq)
Weakly acidic
Phenol>H2O>ethanol
Stability of conjugate base Acids and bases
1. C6H5O−
A lone pairs on oxygen overlaps with π bonding system
Reduce charge density-->stability
2. C2H5OElectron-donating alkyl group
Concentrating negative charge on oxygen
Reactions
1. Breaking of O-H
1. +Alkali-->salt + water
2. +Metal-->salt +H2
2. Substitution
React more readily with electrophile
Lone pair on oxygen--> electron density↑