Aromatic Chemsitry

Question 1

What are arenes

Answer 1

Large family of unsaturated cyclic hydrocarbons

Question 2

What makes benzene different from cyclohexatriene

Answer 2

1. Reaction with bromine:
   Substitution occurs rather than addition
2. Bond length:
   All same bond length rather than a change between C-C and C=C
3. Stability:
   Benzene is more stable due to stabilisation (delocalisation) energy

Question 3

What is the definition of delocalisation (arenes)

Answer 3

The pi electrons are spread over several atoms

Question 4

Describe the structure of benzene

Answer 4

1. Symmetrical planar
2. 3 sigma bonds in each C atom (with two C and one H)
3. 4th electron held in p orbital
4. P orbital overlaps sideways on both neighbouring p orbitals
5. P orbitals fuse together and form delocalised ring above and below planar sigma bonded ring

Question 5

Describe the physical properties of benzene

Answer 5

1. Colourless liquid
2. Non-polar - weak vdw
3. Toxic
4. Distinct aroma
5. Immiscible in water
6. Soluble in non polar solvents

Question 6

What kind of reactions do benzene undertake

Answer 6

Substitution

Question 7

What are the chemical properties of benzene

Answer 7

1. Relatively stable

2. Electrophilic substitution reactions

Question 8

Write the equation for mononitration

Answer 8

See notes

Question 9

What is the electrophile in mononitration

Answer 9

Nitronium ion NO2+

Question 10

How is the nitronium ion produced in mononitration. Write the equations

Answer 10

In situ
Conc sulfuric acid and conc nitric acid
It is the nitrating mixture
See notes for equations

Question 11

Draw the mechanism for mononitration

Answer 11

See notes

Question 12

What must be present for monobromination to occur and what is its general name

Answer 12

Iron (III) Bromide
FeBr3
A halogen carrier catalyst

Question 13

Write the mechanism for monobromination

Answer 13

See notes

Question 14

Describe the key points of monobromination

Answer 14

1. Br2 polarised as approaches ring
2. FeBr3 accepts Br- to form a Br+
3. Br+ attracted to electrons in benzene
4. Br+ covalently bonds to C - disrupts ring
5. Electron in C-H goes back to ring - reform delocalised cloud
6. FeBr4- reacts with H+ to form FeBr3 and HBr

Question 15

Draw the mechanism for alkylation

Answer 15

See notes

Question 16

What is required for alkylation and what is it called

Answer 16

Aluminium chlorine
AlCl3
Halogen carrier catalyst - produces CH3+

Question 17

Write the equation for alkylation what is the byproduct

Answer 17

See notes

HCl

Question 18

What is the equation for acylation

Answer 18

See notes

Question 19

What is required for acylation, what is it and what does it do

Answer 19

Aluminium chloride
Halogen carrier
Catalyst
Generates CH3CO+ which attacks pi system

Question 20

Draw the mechanism for acylation

Answer 20

See notes

Question 21

Compare reactivity of benzene and alkenes

Answer 21

1. Alkenes have C=C (readily attacked), benzene has ring which is more stable
2. Both have pi and sigma bonds
3. Alkenes = addition but benzene = substitution
4. Benzene needs halogen carrier catalyst
5. Benzene reactions are slower

Question 22

How do you prepare methyl 3-nitrobenzoate

Answer 22

See notes