Discuss the physical evidence for the structure of benzene.

State the typical reactions that benzene and cyclohexene undergo with bromine.

State the reagents used to convert benzene to nitrobenzene and the formula of the electrophile formed.

Explain the mechanism for the nitration of benzene, using curly arrows to show the movement of electron pairs.

State the reagents used in the two-stage conversion of nitrobenzene to aniline.

Any two of:
planar «X-ray»

C to C bond lengths all equal
OR
C to C bonds intermediate in length between C–C and C=C

all C–C–C bond angles equal

[2 marks]

benzene: «electrophilic» substitution/S_E
AND
cyclohexene: «electrophilic» addition/A_E

Accept correct equations.

[1 mark]

«concentrated» nitric AND sulfuric acids

⁺NO₂

Accept NO₂⁺.

[2 marks]

curly arrow going from benzene ring to N of ⁺NO2/NO₂⁺

carbocation with correct formula and positive charge on ring

curly arrow going from C–H bond to benzene ring of cation

formation of organic product AND H⁺

Accept mechanism with corresponding Kekulé structures.

Do not accept a circle in M2 or M3.

Accept first arrow starting either inside the circle or on the circle.

M2 may be awarded from correct diagram for M3.

M4: Accept C₆H₅NO₂ + H₂SO₄ if HSO₄^– used in M3.

Fe/Zn/Sn AND HCl/H₂SO₄/CH₃COOH

NaOH/KOH

Accept other suitable metals and acids.

Accept other suitable bases.

Award [1 max] for single-step reducing agents (such as H₂/Pt, Na₂S etc.).

Accept formulas or names.

[2 marks]