Aromatic Chemistry.

Question 1

List the three types of reactions that aromatic compounds can undergo.

Answer 1

Nitration of Benzene , Freidal Crafts acylation and also the reduction of Nitrobenzene into phenyl amines.

Question 2

Give the change in functional group for the nitration of benzene.

Answer 2

Benzene into nitrobenzene

Question 3

Give the electrophile in the nitration of benzene.

Answer 3

NO2 + Ion.

Question 4

Give an equation for the production of the electrophile in the nitration of Benzene.

Answer 4

HNO3 + 2H2SO4 goes into NO2+ 2HSO4- H3O +

Remember the damn hydroxonium Ion.

Question 5

What type of reaction is the production of the electrophile in the nitration of Benzene. State the role of each of the reactants.

Answer 5

This is an acid base reaction that takes place between two typical thought of acids.
The Sulphuric acid acts as an acid and the Nitric acid acts as a base.

Question 6

Give an overall reaction for the nitration of benzene.

Answer 6

See Picture on sheet.

Question 7

Give the mechanism for the nitration of Benzene. State the name also.

Answer 7

See Picture on sheet. Electrophilic substitution of the hydrogen.

Question 8

Give the reagents for the Nitration of Benzene.

Answer 8

Concentrated Nitric acid in the presence of a concentrated sulphuric acid.

Question 9

State the temperature that the Nitration of Benzene should be done under and state what can happen when this temperature is exceeded.

Answer 9

60 degrees Celsius and if the temperature exceeds this then a second Nitro group can be substituted.

Question 10

Give the key use of the product formed from the nitration of Benzene.

Answer 10

Important step in manufacture of TNT, 2-methyl-1.3, 5 trinitrobenzene. And also the formation of amines from which dye is manufactured.

Question 11

Give the change in functional group for a Freidal crafts acylation. reaction.

Answer 11

Benzene into phenyl ketone.

Question 12

Give the reagents for a freidal crafts acylation reaction.

Answer 12

Acyl chloride in the presence of an anhydrous aluminium chloride catalyst.

Question 13

Give the conditions for a freidal crafts acylation reaction.

Answer 13

Heat at 50 degrees Celsius under reflux conditions.

Question 14

Give the reaction that produces the electrophile in a freidal crafts acylation reaction.

Answer 14

AlCl3 + CH3COCl INTO CH3CO+ and AlCl4 -

Question 15

Give the general formula for the organic reactant that can be used in a freidal craft reaction and state , in general terms the electrophile that will be produced from this reactant.

Answer 15

Any acyl chloride can be used. Anything with RCOCl will be able to form the electrophile RCO+.

Question 16

Give the overall reaction for ethanoyl chloride reacting with benzene in the presence of an anhydrous aluminium chloride catalyst.

Answer 16

aromatic benzene reacts with the acyl chloride with a AlCl3 catalyst on the top to produce the ketone and HCl

Question 17

Name the main organic product formed when ethanoyl chloride and benzene undergo a freidal crafts acylation reaction.

Answer 17

Will be phenylethanone.

Question 18

Name and outline a mechanism for Freidal crafts acylation with benzene and ethanoyl chloride.

Answer 18

See the sheet.

Question 19

Give the equation that happens at the end of a freidal crafts acylation reaction , state when you would need to use the two products you have written down. State also what property this shows of a particular species.

Answer 19

AlCl4- + H+ –> AlCl3 + HCl

Shows AlCl3 is a catalyst in the overall reaction so should sit above the arrow as it is regenerated.

Question 20

Why are freidal crafts reactions important in organic chemistry.

Answer 20

They introduce a reactive functional group on to the benzene ring , an acyl functional group , the benzene ring is acylated.

Question 21

Describe the structure of Benzene. Give its molecular formula also.

Answer 21

Six carbons bonded together in a hexagonal ring, with one H bonded to each carbon, the two carbon bonds and one hydrogen is from the sigma bond. There is one unused electron for every carbons p orbital that is perpendicular to the plane. The six p electrons all overlap in a ring stricture above and below the plane of carbon atoms.

Question 22

List off the three main pieces of evidence that confirm benzene exists in a resonance form of the two kekule structures rather than a cyclic triene or an equilibrium between the two.

Answer 22

The carbon carbon bond lengths are the same, double bonds are shorter than single bonds so the hexagon would not be perfect. (From X-ray diffraction).
A cyclic triene should show addition reaction but benzene more readily undergoes electrophilic substitution.
The hydrogenation of cyclohexa-1,3,5-triene from the hydrogenation of cyclohexene shows that benzene is more stable in reality than expected.

Question 23

Explain , with the aid of equations and a diagram why benzene thermodynamically does not exist as cyclohexane-1,3,5-triene but instead exists as a delocalised system.

Answer 23

See the front page of the sheet.
Delocalised benzene is more stable than the theoretical structure by 152kjmol when on enthalpy diagram by use of hydration enthalpies, actual is -208 not -360.

Question 24

Describe the shape of benzene.

Answer 24

120 degrees and planar.

Question 25

Draw 1-chloro-4-methyl benzene.

Answer 25

page 2 of the sheet.

Question 26

Draw 2-methyl-1,3,5-trinitobenzene

Answer 26

page 2 of the sheet .

Question 27

Draw phenylethanone.

Answer 27

Page 2 of the sheet .

Question 28

Draw phenylamine.

Answer 28

page 2 of the sheet.

Question 29

Describe the types of reactions that benzene will generally undergo.

Answer 29

Doesn’t readily undergo addition reactions as this would involve the breaking up of the delocalised system. Due to the high electron density in the delocalised system , benzene instead favours electrophilic substitution reactions as it attracts positive electrophiles.

Question 30

Explain the effect of the benzene ring of the side group for chlorobenzene. State how this affects reactions.

Answer 30

Wont undergo nucleophilic substitution like haloalkanes since electron rich benzene ring repels nucleophiles and the C-Cl is made stronger. delocalisation extends to the lone pair on the Cl.

Question 31

Explain the effect of the benzene ring of the side group for phenol. What properties does this affect in terms of phenol being an alcohol.

Answer 31

Delocalisation makes the C-O bond stronger and O-H bond weaker. phenol os therefore more acidic than an alcohol and does not oxidise so it will not act like one at all. Delecoaliosation extends to the Lone pair on the O.

Question 32

Explain the effect of the benzene ring of the side group for phenylamine.

Answer 32

Delocalisation extents to lone pair on the N of the NH2 to aromatic amines are less basic than aliphatic amines as less able to accept protons if the Lone pair is tangles up in the delocalised system.