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AQA A Level Chemistry > Aromatic Chemistry > Flashcards

Flashcards in Aromatic Chemistry Deck (12)
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1
Q

What are the 4 problems with Kekules suggested structure for benzene? (cyclic with a double bond every other bond)

A

1 - would expect electrophilic addition reactions, but doesn’t react
2 - Would expect 4 isomers of dibromobenzene, however 1,2 and 1,6 models were indistinguishable, so in reality only 3 (irregular = bonds)
3 - enthalpy changes of benzene didn’t match predictions based off double and single bond data
4 - x-ray crystallography should show = to be shorter than - –> actually showed perfect hexagon

2
Q

What did the equilibrium model for benzene suggest?

A

There were 2 forms that rapidly inter-converted

3
Q

What is the name of the accepted benzene model?

A

Delocalised Model

4
Q

What does the delocalised model for benzene show its structure to be?

A

A cyclic C hexagon, with p orbitals above and below. These orbitals are close enough to overlap, and so form a continuous pi bond above and below the planar of the ring

5
Q

What are the conditions for nitration?

A

conc. HNO3
conc H2SO4
50*C

6
Q

How is the nitronium ion generated for nitration?

A

1) HNO3 + H2SO4 –> H2NO3+ + HSO4-

2) H2NO3+ –> NO2+ + H2O

7
Q

What are the uses of nitrobenzenes?

A
As explosives (TNT)
To make aromatic compounds (amines, used to make dyes)
8
Q

What are the conditions for Friedel Crafts acylation?

A

AlCl3 catalyst, dry

9
Q

What are the reactants and products of Friedel-Crafts acylation?

A

Reactants - a benzene-based compound and either acyl chloride or an acid anhydride
Products - An aromatic ketone and either HCl or a carboxylic acid

10
Q

What type of reaction mechanism occurs in Friedel-Crafts acylation?

A

Electrophilic substitution

11
Q

How does the AlCl3 catalyst form the electrophilic ion necessary for Friedel-Craft acylation, and what is the name of this ion?

A

AlCl3 + RCOCl –> AlCl4- + RCO+

RCO+ –> Acyllium ion

12
Q

Describe and explain the difference in stability between the hypothetical cyclohexa-1,3,5-triene and benzene

A

Benzene is more stable
Has 3 double bonds rather than 1, and its double bonds are close enough to overlap, thus allowing the electrons to become delocalised in a pi orbital above and below the ring, which is more stable