6.1 Aromatic Compounds, Carbonyls And Acids

Question 1

Describe Kekule’s model of benzene

Answer 1

Six-membered ring with alternating single and duble bonds between the carbon atoms

Question 2

What are the 3 features of benzene that don’t support Kekule’s model?

Answer 2

• Benzene is resistant to addition reactions unlike alkenes
• Enthalpy chane of hydrogentaion of benzene is more stable than predicted
• All the carbon bonds have the same length instead of 3 short C=C bonds and 3 long C-C bonds

Question 3

What technique was used to find the bond lengths of benzene?

Answer 3

X-ray diffraction

Question 4

What happens to the 4th electron in the p-orbital of each carbon atom in benzene?

Answer 4

It delocalizes to form rings of electron density above and below the molecule

Question 5

How do the rings of electron density affect the stability of benzene?

Answer 5

Makes benzene very stable, even though it is unsaturated (aromatic stability)

Question 6

Is benzene soluble in water? Why?

Answer 6

No because it’s non polar

Question 7

How do you name compounds containing a benzene ring?

Answer 7

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

Question 8

Why is benzene attacked by electrophiles?

Answer 8

High electron density above/below ring due to delocalised electrons

Question 9

1. Whats’ an electrophilic substitution ?

2. What’s a reaction mechanism?

Answer 9

1. a substitution reaction where an electrophile is attracted to an electron-rich atom/ part of a molecule and a new covalent bond is formed by the electrophile accepting an electron pair
2. a model with steps to explain and predict a chemical reaction

Question 10

Nitration of benzene is what type of reaction ?

Answer 10

Electrophilic substitution reaction

Question 11

Which ion is used to nitrate benzene?

Answer 11

NO2+

Question 12

What is the catalyst in nitration of benzene?

Answer 12

Concentrated sulfuric acid

Question 13

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

Answer 13

Conc. H2S04, Conc, HNO3

H2S04 + HNO3 -> HSO4- + NO2+ + H20

Question 14

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

Answer 14

HSO4- + H+ ->H2SO4

Question 15

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

Answer 15

A halogen carrier (AlCl3, FeBr3)

Question 16

Why does benzene not react directly with halogens?

Answer 16

There isn’t enough electron density between the carbon atoms to induce a dipole in a non-polar halogen

Question 17

How is the ALCL3 catalyst reformed?

Answer 17

AlCl4- + H+ -> AlCl3 +HCl

Question 18

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

Answer 18

Use a halogenalkane and AlCl3 to create a electrophile that can attack benzene

Question 19

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

Answer 19

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

Question 20

Why can phenol undergo electrophilic substitution with relative ease?

Answer 20

Because phenol is more reactive than benzene due to p-orbitals electrons from the oxygen add to the delocalised electron ring which increases electron density so it’s more nucleophilic

Question 21

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

Answer 21

Direct group to 2 and 4 position of the ring in electrophilic substitution of aromatic compounds (Donating groups)

Question 22

What is the directing effect of electron withdrawing group NO2 ?

Answer 22

Direct group to the 3 position of the ring in electrophilic substitution of aromatic compounds (Withdrawing group)

Question 23

What is the carbonyl group?

Answer 23

C=O