Benzene and Aromatic Compounds: Flashcards
Revise the delocalized structure of benzene, the evidence for it, naming aromatic compounds and electrophilic substitution.
Benzene and Aromatic Compounds: Flashcards
- QuestionDescribe the bonding in benzene.Answer
A planar ring of six sp² carbons; six p electrons are delocalized above and below the ring.
- QuestionWhat is the C–C bond length in benzene, compared with single and double bonds?Answer
139 pm, between C–C (154 pm) and C=C (134 pm); all six bonds are equal.
- QuestionHow does the enthalpy of hydrogenation show that benzene is extra stable?Answer
Expected 3 × −120 = −360 kJ/mol; actual −208 kJ/mol, so benzene is about 152 kJ/mol more stable.
- QuestionWhy does benzene undergo substitution rather than addition?Answer
Substitution keeps the stable delocalized ring intact; addition would destroy it.
- QuestionDoes benzene decolourize bromine water?Answer
No (unlike alkenes).
- QuestionGive the reagents and conditions for nitrating benzene.Answer
Concentrated HNO₃ and concentrated H₂SO₄, about 50 °C.
- QuestionWhat catalyst is needed to brominate benzene?Answer
FeBr₃ (or iron filings), a halogen carrier.
- QuestionWhat is the electrophile in nitration?Answer
The nitronium ion, NO₂⁺.
- QuestionName C₆H₅CH₃, C₆H₅OH and C₆H₅NH₂.Answer
Methylbenzene (toluene), phenol, phenylamine (aniline).
- QuestionWhat is the catalyst in Friedel–Crafts reactions?Answer
Aluminium chloride, AlCl₃.
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