Aromatic Chemistry
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Molecular formula of benzene
C6H6
What did Kekule dream of?
Benzene’s structure of alternating double and single bonds
What would be the IUPAC name for Kekule’s structure?
Cyclohexatriene
What are the problems with Kekule’s structure?
• Benzene does not decolourise bromine water (if it was unsaturated it should undergo Electrophilic addition) • Benzene bonds are all the same length and intermediate between Normal C-C bonds and C=C bonds
List the different C bonds in order of length
C-C>C-C(benzene) > C=C
How are the electrons arranged in benzene
In a delocalised ring
How to tell the difference between cyclohexane and benzene
Benzene must have a delocalised ring
Describe bonding in Benzene
Each C forms 3 bonds in trigonal planar structure Forth valence (outer e-) in 2p overlaps with 4th e-‘s of adjacent C’s resulting in a ring
What is the thermochemical evidence for delocalisation in Benzene
Expected 🔺H is -360 kJmol-1 Actual 🔺H is -208 kJmol-1 Which is 152 kJmol-1 less exothermic Therefore benzene is more stable than Kekule’s structure due to delocalised ring of e-
What reaction is used to provide evidence for Kekule’s structure being incorrect?
🔺H of hydrogenation of benzene
How to name aromatic compounds if the benzene ring has a functional group attached directly to it
Use benzene suffix
How to name a compound with an R group or ester link attached to the benzene ring
Use the prefix “phenyl”
What is the name used for C chains not including benzene
Aliphatic
Define aromatic
Contains a benzene ring
Define Electrophile
E- pair acceptor
Define nitronium ion
NO2+
What is an acylium ion
O || R-C+
Name of +NO2
Nitronium ion
3 steps for electrophilic substitution
1) generation of electrophile 2) electrophilic substitution 3) regeneration of catalyst
Why is it called electrophilic substitution
H+ substituted for electrophile
What are the conditions and reactants for electrophilic substitution for the notation of benzene What is produced
Concentrated HNO3 and Concentrated H2SO4 50 degrees C Nitrobenzene
Equation for nitration of benzene
Conc. H2SO4 Benzene + HNO3 ————-> water + nitrobenzene
Give 2 steps to produce electrophile for nitration of benzene
H2SO4 protonates HNO3 Protonated nitric acid breaks down to form nitronium ion and water
Give two equations for the generation of electrophile in nitration of benzene
H2SO4 + HNO3—-> H2NO3+ + HSO4- H2NO3+ ——> NO2+ + H2O