ch25

Question 1

What is benzene?

Answer 1

A cyclic hydrocarbon compound C6H6

Question 2

Define arene

Answer 2

An aromatic hydrocarbon containing one or more benzene rings

Question 3

Define aromatic

Answer 3

Any compound containing one or more benzene rings

Question 4

What is the electrophilic addition argument against benzene having the Kekule structure?

Answer 4

Three C=C bonds so it is expected
No reaction with bromine water at room temperature
No other electrophilic addition reactions
Only substitution reactions

Question 5

What is the response to the electrophilic addition argument against benzene having the Kekule structure?

Answer 5

Two forms in rapid equilibrium
Approaching Br-Br not attracted to bonds
Bonds change from C=C to C-C before reaction occurs
Bromine doesn’t react

Question 6

Outline the stability argument against benzene having the Kekule structure

Answer 6

One C=C bond in 6 carbon ring, enthalpy -120kJ/mol
Two C=C bonds in 6 carbon ring, enthalpy -240kJ/mol
Expect 3 C=C bonds to be -360kJ/mol but is actually -208kJ/mol
Delocalisation energy
More stable than expected

Question 7

What causes benzene to have its unexpected properties?

Answer 7

Localised p-orbitals overlap and form delocalised π orbitals above and below the carbon structure (rings)

Question 8

Define electrophile

Answer 8

electron pair acceptor

Question 9

What are the conditions for nitration of benzene?

Answer 9

Benzene + HNO3

with H2SO4 at 50C

Question 10

As halogens cannot react on their own with benzene, what is required?

Answer 10

Halogen carrier

Question 11

Give two examples of chlorine carriers

Answer 11

AlCl3

FeCl3

Question 12

What is formed as a byproduct of halogenation of benzene?

Answer 12

HX

Question 13

What are the two types of Friedel Crafts reactions of benzene?

Answer 13

Alkylation

Acylation

Question 14

Outline alkylation of benzene

Answer 14

Benzene + RCl with FeCl3

Forms alkylbenzene + HCl

Question 15

Outline acylation of benzene

Answer 15

Benzene + RCOCl with FeCl3

Forms Phenylalkanone + HCl

Question 16

Name the mechanism for bromination of benzene

Question 17

Outline electrophilic aromatic substitution

Question 18

How does a nitrating mixture produce an electrophile?

Question 19

How is the H2SO4 catalyst regenerated?

Question 20

How is an electrophile formed in reaction with a halogen carrier?

Question 21

How is the halogen carrier catalyst regenerated?

Question 22

What is the structure of phenol?

Answer 22

A phenol has a hydroxyl group directly bonded to an aromatic ring.

Question 23

What are the products of phenol reacting with NaOH?

Answer 23

form sodium phenoxide and water ( a neutralisation reaction).

Question 24

Why does phenol not react with Na2CO3?

Answer 24

phenol is a weak acid.

Question 25

What is formed on reaction of phenol with excess Br2?

Answer 25

2,4,6-tribromophenol and HBr

Question 26

What are the reaction conditions of bromination of phenol?

Answer 26

room temp. halogen carrier not required

Question 27

Why does phenol react so readily with bromine?

Answer 27

The electrons in the lone pair in a p-orbital on the oxygen atom in the phenol O-H group can delocalise into the pi-system of bonds in the aromatic ring. This increases the electron density of the benzene ring in phenol making it more able to polarise and attract electrophiles.

Question 28

Where do the NH2 and OH groups direct on benzene?

Answer 28

2,4 ortho and para

Question 28

Where does the NO2 group direct on benzene?

Answer 28

3 directing group (meta)