Aromatic Compounds Flashcards
conditions and reagents for the nitration of benzene
sulphuric acid
50°C
what happens if the temperature in the nitration of benzene rises above 50°C
might form dinitrobenzene
what is nitrobenzene used for
a starting material in the preparation of dyes, pharmaceuticals, and pesticides
what is the electrophile in the nitration of benzene
NO2+
3 steps in the nitration/halogenation of benzene
electrophile formation
attacks the benzene ring
regeneration of the catalyst
how does the electrophile attack the benzene ring in the nitration of benzene
NO2+ accepts a pair of electrons from the benzene ring to form a dative covalent bond.
The organic intermediate formed is unstable, and breaks down to form nitrobenzene and a H+ ion
A stable benzene ring is reformed
How is the catalyst regenerated
H+ ion reacts with HSO4- ion to regenerate
what is the catalyst called in the halogenation of benzene
halogen carrier/Friesdel-Crafts
AlBr3
reagents and conditions for the halogenation of benzene
halogen carrier
room temp and pressure
what is alkylation of benzene
substitution of a h atom
haloalkane and benzene react in the presence of AlCl3 which acts as a halogen carrier
what is the alkylation reaction sometimes called
Friedel-Crafts alkylation
what is acylation of benzene
benzene reacts with acyl chloride in the presence of AlCl3 catalyst
forms a aromatic ketone
electrophilic substitution
name the molecule when they have these groups in benzene: chloro- nitro- hydroxy- methyl- amino- carboxylic acid
chlorobenzene nitrobenzene phenol methylbenzene/toluene phenylamine/aniline benzenecarboxylic acid/benzoic acid
which groups are assumed to occupy position 1
OH of phenol or CH3 of methylenzene
when is benzene the substituent
when it is attached to an alkyl chain with a 7+ carbons= phenyl
what reaction does benzene undergo
electrophilic substitution
what is the purpose of alkylation
to increase the number of carbon atoms in a compound by forming C-C bonds
properties of phenol
colourless solid at room temp- hydrogen bonds
dissociates in water
are phenols stronger acids than alcohols?
yes
ethoxide ion readily accepts proton forming ethanol- positive inductive effect
what happens when phenol reacts with aqueous alkalis
a salt forms
as phenol is a weak acid, it will react readily with the strong alkali sodium hydroxide to form sodium phenoxide
why are phenols useful
can make phenyl esters which make polyesters
why doesn’t phenol react with sodium carbonate solution
sodium carbonate isn’t a strong enough base
2 types of phenol reactions
reactions of the phenol group
substitution in the aromatic ring
what is the bromination of phenol
phenol + 3Br2 –> phenolBr3 + 3HBr
what happens when there is NO2 on the aromatic ring
the ring reacts less readily with electrophiles, so requires a halogen carrier and high temp as it reacts slower than benzene
phenol and 3Br2- what happens
decolourises and a white precipitate may be formed
what products are formed when phenol and NaOH react
sodium phenoxide
no observable reaction
what happens when phenol and NaOH react
sodium phenoxide and water
no observable reaction
what happens when phenol and 3Br2 react
2,4,6 tribromophenol and 3HBR
decolourises bromine and white precipitate may form
properties of benzene that are determined by the stsructure
all carbon-carbon bonds same length can be attacked by electrophile due to density undergoes substitution not addition is planar stable structure
why does phenol react differently from benzene
electrons from one of oxygens p-orbitals overlap with the benzene rings delocalised system, increasing its electron density
this makes the ring more likely to be attacked by electrophiles
Which is most reactive
Benzene
Phenol/phenylamine
Nitrobenzene
Phenol/phenylamine
Benzene
Nitrobenzene
Describe the reactivity of benzene
Moderate temp (50oC)
Catalyst
Electrophilic substitution
Describe the reactivity of nitrobenzene
Deactivating 3 directing Less readily reacts with electrophiles Strong electronegativity of nitrogen so decreases availability of electrons so less dense High temp Halogen carrier needed
Describe the reactivity of phenol/phenylamine
Activating
2,4,6 directing
Lone pairs on OH/NH2 interact with ring making it more electron dense
Increased availability of electrons from lone pairs
describe the bonding in a benzene molecule
3 electrons from each C is used to form sigma bonds to 2C and H
delocalised system of electrons
pi bonds above and below plane of C atoms
p-orbital overlaps with electrons from adjacent C atoms
how does the kekule model differ from the accepted version
contains alternating double/single bonds
evidence that led to reject the kekule model
benzene less reactive than predicted- halogenation of benzene
the enthalpy change of benzene is lower than expected
model doesn’t show that all C-C bonds are the same length
what substances and conditions used to form nitrobenzene
concentrated nitric and sulfuric acid
less than 50 degrees for no further substitutions
what reacts with sodium carbonate
ethanoic acid would fizz
phenol doesn’t as it is too much of a weak base
what can ethanoic acid react with
alkalis and carbonates
what happens with bromine and benzene vs cyclohexene and bromine
benzene and bromine- C-H bond breaks and electrons donated to ring
stable delocalised structure regenerated
benzene and cyclohexene- carboation unstable
