Aromatic hydrocarbons are compounds that contain
A only single bonds
B only double bonds
C conjugated planar ring with delocalised π-electrons
D triple bonds only
Aromaticity requires planarity, conjugation and delocalised π-electrons.
Benzene has how many π-electrons
A 2
B 4
C 6
D 8
Benzene follows Hückel’s rule (4n+2, n=1).
Hückel’s rule for aromaticity is
A nπ electrons
B 4nπ electrons
C (4n+2)π electrons
D 6π electrons only
Aromatic systems must satisfy this condition.
Benzene is unusually stable due to
A inductive effect
B resonance
C hyperconjugation
D steric effect
Delocalisation of π-electrons gives resonance energy.
Benzene prefers substitution over addition because
A addition is faster
B substitution preserves aromaticity
C addition gives stable products
D substitution lowers activation energy
Addition destroys aromatic character.
The general mechanism of electrophilic aromatic substitution involves
A nucleophile attack
B free radical attack
C formation of σ-complex
D carbanion formation
Also called arenium ion or Wheland intermediate.
The electrophile in nitration of benzene is
A NO₂⁻
B NO₂•
C NO₂⁺
D NO₃⁻
Nitronium ion is generated from HNO₃ + H₂SO₄.
Which acid acts as catalyst in nitration
A HNO₃
B HCl
C H₂SO₄
D H₃PO₄
Sulphuric acid generates the electrophile.
Halogenation of benzene requires a catalyst because
A halogens are weak nucleophiles
B halogens are weak electrophiles
C benzene is unreactive
D halogens are inert
Lewis acid activates halogen.
Catalyst used in chlorination of benzene is
A ZnCl₂
B FeCl₃
C NaCl
D HCl
Acts as Lewis acid.
Sulphonation of benzene introduces
A –NO₂
B –SO₃H
C –CHO
D –COOH
Oleum or fuming sulphuric acid is used.
Sulphonation of benzene is reversible because
A σ-complex is unstable
B SO₃H group is bulky
C reaction depends on temperature
D benzene is non-polar
Heating with dilute acid removes –SO₃H group.
Friedel–Crafts alkylation introduces
A –NO₂
B alkyl group
C –COOH
D –CHO
Uses alkyl halide + AlCl₃.
Friedel–Crafts acylation introduces
A alkyl group
B acyl group
C nitro group
D sulpho group
Uses acid chloride or anhydride.
Friedel–Crafts acylation does not cause rearrangement because
A carbocation is not formed
B acylium ion is unstable
C reaction is slow
D AlCl₃ blocks rearrangement
Acylium ion is resonance-stabilised.
Friedel–Crafts reaction does not occur with
A benzene
B toluene
C chlorobenzene
D nitrobenzene
Strongly deactivated ring.
Alkyl groups on benzene are
A deactivating
B meta-directing
C activating and o,p-directing
D deactivating and o,p-directing
+I and hyperconjugation increase electron density.
Nitro group on benzene is
A activating
B o,p-directing
C meta-directing
D neutral
−I and −R effects withdraw electrons.
Which group is o,p-directing but deactivating
A –CH₃
B –NH₂
C –Cl
D –OH
Halogens donate by resonance but withdraw inductively.
Activating groups increase reaction rate by
A stabilising σ-complex
B destabilising benzene
C increasing molecular weight
D forming radicals
Lower activation energy for substitution.
Deactivating groups decrease rate because they
A destabilise benzene
B destabilise σ-complex
C increase resonance energy
D increase aromaticity
Electron withdrawal makes intermediate less stable.
Which substituent is strongly activating
A –NO₂
B –CN
C –NH₂
D –COOH
Strong +R effect.
Which compound undergoes EAS fastest
A nitrobenzene
B chlorobenzene
C benzene
D aniline
–NH₂ strongly activates the ring.
Orientation in EAS is determined by
A steric hindrance only
B inductive effect only
C resonance effect
D molecular mass
Stability of σ-complex at different positions.
Toluene undergoes nitration mainly at
A meta-position
B ortho and para positions
C para-position only
D ortho-position only
–CH₃ is o,p-directing.
Why para product is often major over ortho
A higher activation energy
B resonance instability
C steric hindrance at ortho position
D inductive effect
Less crowding at para position.
Side-chain chlorination of toluene occurs in presence of
A FeCl₃
B AlCl₃
C UV light
D H₂SO₄
Free radical substitution at benzylic position.
Side-chain chlorination proceeds via
A carbocation
B carbanion
C free radical
D σ-complex
Homolytic cleavage under UV.
Ring chlorination of toluene requires
A UV light
B FeCl₃
C NaOH
D peroxide
Electrophilic substitution.
Benzylic position is highly reactive because
A carbocation is stable
B carbanion is stable
C radical is resonance stabilised
D steric effect is minimum
Benzylic radical is delocalised.
Oxidation of toluene with KMnO₄ gives
A benzyl alcohol
B benzaldehyde
C benzoic acid
D benzene
Side-chain oxidised completely.
Which compound does not undergo Friedel–Crafts reaction
A benzene
B anisole
C chlorobenzene
D nitrobenzene
Strong deactivation.
Aromatic hydrocarbons generally resist
A substitution
B oxidation
C addition
D nitration
Addition destroys aromaticity.
Which species attacks benzene in EAS
A nucleophile
B electrophile
C free radical
D base
π-electrons attract electrophiles.
σ-Complex formation is
A slow step
B fast step
C reversible step
D termination step
It is rate-determining step.
Loss of proton from σ-complex restores
A conjugation
B aromaticity
C hybridisation
D polarity
Final step regenerates benzene ring.
Which group directs substitution to meta position
A –OH
B –CH₃
C –NO₂
D –NH₂
Strong electron withdrawal destabilises o,p σ-complex.
Chlorobenzene is less reactive than benzene because
A steric hindrance
B −I effect of Cl
C lack of resonance
D absence of π-electrons
Inductive withdrawal dominates.
However chlorobenzene is o,p-directing due to
A inductive effect
B resonance donation
C hyperconjugation
D steric effect
Lone pair donation directs substitution.
Which reagent introduces –CHO group into benzene
A Reimer–Tiemann
B Gattermann–Koch
C Friedel–Crafts
D Sandmeyer
Uses CO + HCl + AlCl₃/CuCl.
Reimer–Tiemann reaction is shown by
A benzene
B phenol
C toluene
D aniline
Introduces –CHO group ortho to –OH.
Phenol undergoes bromination without catalyst because
A bromine is strong electrophile
B ring is highly activated
C steric effect
D resonance is absent
–OH strongly donates electrons.
Bromination of phenol in water gives
A mono-bromophenol
B dibromophenol
C tribromophenol
D bromobenzene
Strong activation leads to polysubstitution.
Aniline is protected before nitration by
A acetylation
B oxidation
C reduction
D halogenation
Controls excessive activation.
Acetanilide directs substitution to
A meta only
B ortho and para
C para only
D meta and para
–NHCOCH₃ is o,p-directing.
Which compound shows maximum resonance energy
A cyclohexane
B benzene
C ethene
D cyclobutadiene
Fully aromatic and stabilised.
Anti-aromatic compounds are
A highly stable
B moderately stable
C unstable
D non-planar
4n π-electron systems are destabilised.
Which system is anti-aromatic
A benzene
B cyclobutadiene
C cyclohexane
D toluene
Has 4 π-electrons.
Aromatic hydrocarbons generally have
A high heat of hydrogenation
B low resonance energy
C low heat of hydrogenation
D no stability
Indicates high stability.
Correct statement is
A Aromatic compounds follow addition reactions
B Aromaticity depends only on number of carbons
C Electrophilic substitution preserves aromaticity
D All substituted benzenes are deactivated
Key feature of aromatic chemistry.