Aromatic Chemistry Flashcards
1
Q
why is the hypothetical structure for benzene not accepted (cyclohexatriene)
A
- benzene doesn’t decolourise bromine water)
- all the C-C bonds in benzene are the same length
- the actual enthalpy of hydrogenation of benzene is less exothermic than the hypothetical due to benzene being more stable than originally thought
2
Q
describe the actual structure of benzene
A
- each carbon forms 3 bonds in the trigonal planar structure
- fourth valence electron forms a π bond by overlapping with the 2p electrons on the adjacent carbon atoms resulting in a ring of delocalised electrons
3
Q
why is the actual structure of benzene more stable than the hypothetical structure
A
- the π electrons in the C=C bond are delocalised around the benzene ring causing for extra stability
4
Q
what are the reactants, conditions and mechanism of the nitration of benzene
A
- reactants - concentrated HNO₃ and concentrated H₂SO₄ catalyst
- condition - 50°C
- mechanism - electrophilic substitution
5
Q
what is the equation of the formation of a NO₂⁺ electrophile during the nitration of benzene
A
HNO₃ + H₂SO₄ → HSO₄⁻ + NO₂⁺ + H₂O
6
Q
what is a use of nitrobenzene
A
- can be used in the preparation of azo dyes by reducing nitro group to an amine
- reagent = HCl
- condition = Tin Catalyst
- equation = C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O
7
Q
why is methylbenzene more reactive than benzene
A
- methyl group pushes electronegativity onto ring of delocalised electrons ( positive inducing effect )
- this increases electron density in the ring therefore there is a stronger attraction to the electrophile
8
Q
what are the reagents, conditions and mechanisms in a Friedel-Crafts Acylation Reaction
A
- reagents = benzene and acyl chloride
- condition = AlCl₃ catalyst
- mechanism = Electrophilic Substitution
9
Q
what is the equation for the formation of an acylium ion in a Friedel-Crafts Acylation Reaction
A
RCOCl + AlCl₃ → RC⁺O + AlCl₄⁻
