6.1.1- Aromatic Compounds

Question 1

What is formula of Benzene?

Answer 1

C6H6

Question 2

What is empirical formula of benzene?

Answer 2

CH

Question 3

What is state of benzene at room temperature?

Answer 3

Liquid

Question 4

What is the bond angle of benzene?

Answer 4

120 degrees

Question 5

What are the features of benzene that don’t support Kekule’s model?

Answer 5

• Benzene is resistant to addition reactions
• Enthalpy of 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 benzne?

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

What 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 the NO2+ ion generated? (conditions and equations)

Answer 17

Concentrated H2SO4 and HNO3
H2SO4 + HNO3 -> H2NO3+ + HSO4-
H2NO3+ -> H2O + NO2+
Overall: H2SO4 + HNO3 -> HSO4- + NO2+ + H2O

Question 18

How is the H2SO4 catalyst regenerated in nitration of benzne?

Answer 18

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

Question 19

What type of catalyst is used for a Friedel-Crafts reaction?

Answer 19

A halogen carrier ~(e.g. AlCl3)

Question 20

Why does benzene not react directly with halogens?

Answer 20

The aromatic ring is too stable

Question 21

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

Answer 21

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

Question 22

How is the AlCl3 catalyst reformed?

Answer 22

AlCl4- + H+ -> HCl + AlCl3 (H+ from benzene)

Question 23

How could you use a Friedel-Crafts mechanism to add a methyl group to a benzene ring?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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 to phenol

Question 26

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

Answer 26

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

Question 27

What is the directing effect of electron withdrawing group NO2?

Answer 27

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