What type of hydrocarbon is benzene classified as?
Aromatic hydrocarbon
Aromatic compounds contain a benzene ring with delocalised electrons.
What is the shape of the benzene molecule?
Planar hexagon
All carbon atoms lie in the same plane with bond angles of about 120°.
Fill in the blank:
In benzene, all carbon–carbon bond lengths are _______ between single and double bonds.
intermediate
The bonds are all the same length due to electron delocalisation.
True or False:
Benzene contains alternating single and double bonds that remain fixed in position.
False
The π electrons are delocalised around the ring.
What type of electrons are delocalised in the benzene ring?
p electrons
These electrons form a delocalised π system above and below the ring.
True or False:
Delocalisation of electrons increases the stability of benzene.
True
Delocalisation lowers the overall energy of the molecule.
Fill in the blank:
The hypothetical molecule with alternating double bonds used for comparison with benzene is ______-______.
cyclohexa-1,3,5-triene
Benzene is more stable than this theoretical structure.
What thermochemical measurement provides evidence for benzene’s extra stability?
Enthalpy of hydrogenation
Benzene releases less energy than expected when hydrogenated.
True or False:
Benzene undergoes addition reactions easily like alkenes.
False
Addition would break the delocalised electron system.
Fill in the blank:
Benzene usually reacts by _______ reactions rather than addition reactions.
substitution
Substitution preserves the aromatic ring.
Why are substitution reactions preferred over addition reactions in benzene?
Preserve delocalisation
Addition would destroy the stable aromatic system.
What feature of benzene bonding explains its unusual stability?
Electron delocalisation
The π electrons are spread evenly over the entire ring.
What type of reaction commonly occurs when benzene reacts with electrophiles?
Electrophilic substitution
A hydrogen atom on the benzene ring is replaced by another group.
Why does benzene prefer substitution reactions rather than addition reactions?
Preserve aromatic stability
Addition would disrupt the delocalised π electron system.
Fill in the blank:
In electrophilic substitution, the benzene ring acts as a source of _______.
electrons
The π electron cloud attacks the electrophile.
True or False:
Electrophiles are electron pair acceptors.
True
They are attracted to regions of high electron density.
What reaction introduces a nitro group into a benzene ring?
Nitration
This reaction forms nitrobenzene.
True or False:
Nitration of benzene requires a mixture of concentrated nitric and sulfuric acids.
True
Sulfuric acid acts as a catalyst and generates the nitronium ion electrophile.
Fill in the blank:
The electrophile in benzene nitration is the _______ ion.
nitronium
The ion has the formula NO2+.
What role does concentrated sulfuric acid play in nitration?
Catalyst
It helps generate the nitronium ion from nitric acid.
True or False:
Friedel–Crafts acylation introduces an acyl group onto a benzene ring.
True
The reaction forms a ketone attached to the ring.
Fill in the blank:
In Friedel–Crafts acylation, the catalyst commonly used is _______.
AlCl3
Aluminium chloride helps generate the electrophile.
What type of compound is produced when benzene undergoes acylation?
Phenyl-ketone
The benzene ring becomes bonded to a carbonyl-containing group.
Why are nitration and acylation important in industrial chemistry?
Synthetic intermediates
They produce compounds used in explosives, dyes and pharmaceuticals.
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3.1.1 Atomic structure50
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3.1.2 Amount of substance47
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3.1.3 Bonding90
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3.1.4 Energetics62
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3.1.5 Kinetics55
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3.1.6 Equilibria & Kc24
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3.1.7 Redox equations17
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3.1.8 Thermodynamics27
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3.1.9 Rate equations24
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3.1.10 Kp12
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3.1.11 Electrode potentials46
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3.1.12 Acids and bases69
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3.2.1 Periodicity22
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3.2.2 Group 2 metals24
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3.2.3 Group 7 (halogens)31
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3.2.4 Period 3 oxides35
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3.2.5 Transition metals95
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3.2.6 Ions in aqueous solution39
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3.3.1 Intro to organic chemistry42
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3.3.2 Alkanes49
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3.3.3 Halogenoalkanes36
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3.3.4 Alkenes36
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3.3.5 Alcohols43
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3.3.6 Organic analysis36
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3.3.7 Optical isomerism12
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3.3.8 Aldehydes & ketones20
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3.3.9 Carboxylic acids & derivatives25
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3.3.10 Aromatic chemistry29
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3.3.11 Amines41
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3.3.12 Polymers24
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3.3.13 Amino acids, proteins, DNA61
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3.3.14 Organic synthesis12
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3.3.15 NMR spectroscopy14
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3.3.16 Chromatography12
