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 = 120o

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

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

Answer 12

It is a carcinogen

Question 13

How do you name compounds
containing a benzene ring?

Answer 13

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

Question 14

Why is benzene attacked by
electrophiles?

Answer 14

High electron density above/below ring
due to delocalised electrons

Question 15

Nitration of benzene is what
type of reaction?

Answer 15

Electrophilic substitution reaction

Question 16

Which ion is used to nitrate
benzene?

Answer 16

NO₂+

Question 17

What is the catalyst in nitration
of benzene?

Answer 17

Sulfuric acid
H₂SO₄

Question 18

How is this NO₂+ ion
generated? (conditions and
equations)

Answer 18

Concentrated H₂SO₄
and concentrated HNO₃
.

Overall:
H₂SO₄ + HNO₃ → HSO₄(-) + NO₂(+) + H₂O

Question 19

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

Answer 19

HSO₄(-) + H(+) → H₂SO₄
(H+ from benzene ring)

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

Write the equation for the reaction
between phenol with dilute nitric
acid.

Answer 26

Phenol + Nitric acid to either (2 or 4) nitrophenol

Question 27

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

Answer 27

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 28

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

Answer 28

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

Question 29

What is the directing effect of
electron withdrawing group NO2
?

Answer 29

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