3.3.10 - Aromatic chemistry

Question 1

What is an arene?

Answer 1

Compound which contains benzene rings as part of the structure

Question 2

Draw the electrophilic substitution mechanism (NO2 nucleophile)

Answer 2

Attacked towards electrophile, ring partially destroyed (positively charged), H bond restores ring, H+ formed.

Question 3

Aromatic bonding (6 marker) - describe the bonding in benzene, why is it more stable than cyclohexatriene

Answer 3

Carbon forms 3 covalent bonds and has free electron to overlap into a delocalised electron cloud.

Bonds are all planar and equal, with 120” bond angles

Cyclohexatrine deltaH hydrogenation is -360
Benzene is lower in energy/more stable

Question 4

Describe Friedels-Craft Acylation

Answer 4

Ring attracted to carbocation (double bond with oxygen)
H+ electron repairs ring
AlCl4 attracted to the hydrogen
Halogen forms bond with hydrogen repairer, i.e forming HCl and AlCl3

Question 5

Describe nucleophilic addition-elimination

Answer 5

Lone pair on Nitrogen attacks carbon, double bond forms oxygen lone pair.

Oxygen reforms double, bond given to halogen

Hydrogen given to nitrogen, another amine joins it

Question 6

Freidel-Crafts conditions

Answer 6

AlCl3 catalyst
Heated under reflux under non-aqueous solvent

Question 7

Nitrobenzene (electrophilic substitution) formation conditions

Answer 7

H2S04 and HN03
55 degrees

Question 8

State the reaction equation for sulfuric acid and nitric acid to make the NO2+ intermediate

Answer 8

HNO3 + H2SO4 —> NO2+ + HSO4- + H2O

Question 9

Why can’t benzene join with Br2?

Answer 9

In benzene, pi electrons are delocalised, low electron density means it can’t polarise the Br2 bond

Question 10

Ester (when hydrolysed with water) forms…

What acid catalyst is used?

Answer 10

Carboxylic acid + alcohol (dilute H2SO4/HCL catalyst)

Question 11

Ester (when hydrolysed with NaOH) forms?

Answer 11

Carboxylic acid salt (no H but Na+ instead) + alcohol

Question 12

Carboxylic acid salt + HCL =

Answer 12

Carboxylic acid + NaCl

Question 13

What is the name of the mechanism for the formation of nitrobenzene?

Answer 13

Electrophilic substitution

Question 14

Reaction for making CH3CO+

Answer 14

CH3COCl + AlCl3 —–> (CH3CO+) + (AlCl4-)

Question 15

What are the conditions to go from nitrobenzene to phenylamine?

What type of reaction is this?

Answer 15

• Sn
• Conc HCl

Reduction reaction

Question 16

The hydrogenation value of 1-3 cyclohexatriene is not exactly double, what is it (roughly) and why?

Answer 16

• 200
• Double bonds separated by single bond
• Close enough to allow p orbital electron overlap

Question 17

What are the conditions for forming methylbenzene from benzene?

Answer 17

• CH3Cl
• AlCl3 catalyst

SImilar to Friedel-Crafts

Question 18

Why does sodium benzoate dissolve in water and not benazoic acid? (2)

Answer 18

• Sodium benzoate is ionic
• Benzoic acid has polar COOH gorup, but benzene ring is non-polar

Question 19

Why is reflux used in the hydrolysis of an ester?

Answer 19

Ensures none of the reactant vapour escapes