6.1.1: Aromatic compounds

Question 1

What is the structure and formula of Benzene?

Answer 1

C6H6

Question 2

What is the empirical formula of benzene?

Answer 2

CH

Question 3

What is the state of benzene at room temperature?

Answer 3

liquid

Question 4

What is the bond angle of benzene?

Answer 4

Bond angle = 120 degrees

Question 5

What are the 3 features of benzene that don’t

support Kekule’s model?

Answer 5

● Benzene is resistant to addition reactions
● Enthalpy change of hydrogenation of benzene is more stable than predicted
● All the carbon bonds are same length

Question 6

What technique was used to find the bond lengths of

benzene?

Answer 6

X ray diffraction

Question 7

What happens to the 4th electron in the p-orbital of

each carbon atom in benzene?

Answer 7

It delocalises to form rings of electron
density above and below the hexagon,
forming rings of delocalised electron
density above/below the hexagon.

Question 8

How do the rings of electron density affect the

stability of Benzene?

Answer 8

Makes benzene very stable, even though

it is unsaturated (aromatic stability)

Question 9

Why does benzene have a relatively high melting

point?

Answer 9

Close packing of flat hexagonal

molecules when solid

Question 10

Is benzene soluble in water? Explain why?

Answer 10

No because it is non polar

Question 11

Dangers of benzene - why it is not used in schools?

Answer 11

It is a carcinogen

Question 12

How do you name compounds containing a benzene

ring?

Answer 12

-benzene, or phenyl- ; can designate
position on ring using numbers if there is
more than one substituent

Question 13

Why is benzene attacked by electrophiles?

Answer 13

High electron density above/below ring

due to delocalised electrons

Question 14

Nitration of benzene is what type of reaction?

Answer 14

Electrophilic substitution reaction

Question 15

Which ion is used to nitrate benzene?

Answer 15

NO2+

Question 16

What is the catalyst in nitration of benzene?

Answer 16

Sulfuric acid

Question 17

How is this NO2+ ion generated? (conditions and

equations)

Answer 17

Concentrated H2SO4 and concentrated HNO3.
H2SO4 + HNO3 → H2NO3+ + HSO4-
H2NO3+ → H2O + NO2+
Overall: H2SO4 + HNO3 → HSO4- + NO2+ + H2O

Question 18

How is the H2SO4 catalyst regenerated in the nitration of benzene?

Answer 18

HSO4- + H+ → H2SO4

H+ from benzene ring

Question 19

Write an overall equation for

the nitration of benzene.

Answer 19

C6H6 + HNO3 → C6H5NO2 + H2O

Question 20

What type of catalyst is used for a Friedel-Crafts

reaction?

Answer 20

A halogen carrier (e.g. AlCl3)

Question 21

Why does benzene not react directly with halogens?

Answer 21

The aromatic ring is too stable

Question 22

What is happening when AlCl4- is formed in terms of electrons?

Answer 22

The lone pair of electrons on the chlorine atom is forming a coordinate bond to Al

Question 23

How is the AlCl3 catalyst reformed?

Answer 23

AlCl4- + H+ → HCl + AlCl3

(H+ from benzene)

Question 24

How could you use a Friedel-Crafts mechanism to

add a methyl group to a benzene ring?

Answer 24

Use a halogenoalkane and AlCl3 to
create an electrophile that can attack
benzene

Question 25

What reactions can you carry out to show the weak acidity of

phenol?

Answer 25

A neutralisation reaction with NaOH occurs
but absent when you react phenol with
carbonates

Question 26

What is the relative ease of electrophilic substitution of phenol
compared to benzene and why?

Answer 26

It is easier for electrophilic substitution to occur with
phenol because oxygen lone pair of electrons from
the -OH group are partially delocalised into ring
therefore this increases the electron density of the
ring thus electrophiles are more attracted phenol

Question 27

What is the directing effect of electron donating groups OH and NH2?

Answer 27

They direct group to the 2 and 4 position of the ring in electrophilic substitution of aromatic compounds

Question 28

What is the directing effect of electron withdrawing group NO2?

Answer 28

NO2 directs atoms to the 3 position of the ring in electrophilic substitution of aromatic compounds