A Level Chemistry Chapter 25 Benzene and its compounds Detailed Summary Note including the topics - reaction of arenes, Friedel-Crafts reactions, aromatic stabilisation, reactivity of halogenoalkanes and halogenoarenes, phenols, and relative acidities
reaction of arenes
very stable due to the delocalisation of pi electrons in the ring
(negative charge is spread out over the molecule)
substitution
halogenation reactions are examples of electrophilic substitution
-reacts with Cl2 in the presence of anhydrous AlCl3 catalyst
-reacts with Br2 in the presence of anhydrous AlBr3 catalyst
Cl2 or Br2 acts as an electrophile and replaces a hydrogen atom
catalyst is required due to the stability of the benzene structure
substituents that are already present on the arenes can affect
where substitution of the hydrogen atom on the arene takes place
-electron-donating substituents donate electron density into the pi
system of the benzene ring, making it more reactive
-electron-withdrawing substituents remove electron density from
the pi system in the benzene ring, making it less reactive
electron-donating alkyl
group pushes the electron
density into the benzene
ring - becomes more
reactive
eg) alkylarenes such as
methylbenzene undergo
halogenation on the 2
or 4 position due to the
electron-donating alkyl group
-multiple substitutions occur when excess halogen is used
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nitration
a type of substitution reaction where a nitro (-NO2) group replaces
a hydrogen atom on the arene
-benzene is reacted with a mixture of concentrated nitric acid and
concentrated sulfuric acid at a temperature between 25 and 60 C O
overall reaction
Friedel-Crafts reactions
electrophilic substitution to turn arenes into more reactive compounds
so that they could be used as starting materials for the synthesis
of other organic compounds
1) Friedel-Crafts alkylation
an alkyl chain is substituted into the benzene ring
overall reaction
Copyright 2021. 해움. All rights reserved.
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