Aromatics

Question 1

Explain delocalisation

Answer 1

The 4th electron of each carbon is in a Pi orbital. These electrons overlap and are delocalised (spread over more than 2 atoms) which creates an area of electron density above and below the benzene ring.

Question 2

Explain how delocalisation affects the molecules stability

Answer 2

The delocalisation of electron makes benzene very stable, sometimes referred to a aromatic stability

Question 3

Describe the bonding and bond length of benzene

Answer 3

Overall each carbon has 3 electrons making its bond length between that of a single and double bond

Question 4

Name the four anomalies in Kekule’s structure that proved it was false.

Answer 4

1. Only 3 out of 4 isomers were found to exist (1,6-Dibromobenzene could not be found.
2. Benzene was less relative than molecules with C=C such as alkenes
3. When hydrogenated benzene was 152 KJ/mol less exothermic than the unsaturated ring structure
4. All carbon carbon bonds were equal in length (shorter than a double, but longer than a single)

Question 5

Compound name with: CH3

Answer 5

Methylbenzene

Question 6

Compound name with: Cl

Answer 6

Chlorbenzene

Question 7

Compound name with: NO2

Answer 7

Nitrobenzene

Question 8

Compound name with: C2H5

Answer 8

Ethylbenzene

Question 9

Compound name with: OH

Answer 9

Phenol

Question 10

Compound name with: CH2OH

Answer 10

Phenylmethanol

Question 11

Compound name with: NH2

Answer 11

Aminobenzene

Question 12

Compound name with: COOH

Answer 12

Benzoic Acid

Question 13

Compound name with: - C -H
||
O

Answer 13

Phenylmethanal

Question 14

What causes Electrophilic Substitution in benzene

Answer 14

A high electron density above and below the benzene ring which attracts electrophiles

Question 15

Describe Nitration

Answer 15

A nitro group replaces one of the hydrogens. The electrophile is the NO2+

Question 16

How is the nitro group required for nitration made

Answer 16

Mixing concentrated Nitric and sulphuric acid together at 50 degrees Celsius

H2SO4 + HNO3 [H2NO3]+ + HSO4-
[H2NO3]+ NO2+ + H2O

Question 17

Why is Nitration important

Answer 17

It’s an important step in forming explosives such as TNT

Also the first step in making Amines which are used in industrial dyes

Question 18

Describe Benzenes basic structure

Answer 18

A planar molecule with no double bonds

Question 19

Describe the two reactions required to convert Nitobenzene to Aminobenzene

Answer 19

1. Electrophilic addition with HCL to form a halobenzene

2. Nucleophilic substitution with Ammonia to form an Aminobenzene

Question 20

Describe a Friel Crafts Acylation Reaction

Answer 20

It uses Aluminium Chloride (AlCl3) as a catalyst. It’s a substitution reaction in which an RCO group provided by Acyl Chloride is substituted for a hydrogen

Question 21

What are the equations for the formation of RCO and the reformation of AlCl3 in a Friel Crafts Acylation reaction

Answer 21

RCOCl + AlCl3 —> RCO+ + AlCl4-

AlCl4- + H+ —> AlCl3 + HCL