Aromatic Compounds

Question 1

What’s the simplest aromatic hydrocarbon?

Answer 1

Benzene

Question 2

Describe basic properties of benzene

Answer 2

• colourless
• sweet smelling
• highly flammable
• found in crude oil
• carcinogen (cancer causing)

Question 3

Evidence that disproves Kekulé model

Answer 3

• X-ray diffraction = bond length in between single and double bond
• hydrogenation is less exo than expected (comparing to cyclohexene)
• only reacts w/Br2 w/ high temp + halogen carrier catalyst

Question 4

Nitration of benzene

Answer 4

• H2SO4 + 50 degrees
• H2O bath = maintain steady temp
• electrophile = NO2+
• intermediate = unstable
• electrophilic substitution

Question 5

What happens if reaction > 50 degrees in nitration of benzene

Answer 5

Further substitution

Question 6

Uses of nitrobenzene

Answer 6

• dyes
• pharmaceuticals
• pesticides
• paracetamol

Question 7

Bromination of benzene

Answer 7

• room pressure + temp + halogen carrier catalyst

Question 8

Why is a halogen carrier catalyst necessary?

Answer 8

Benzene = too stable to react w/ non-polar bromine molecule

Question 9

Alkylation reaction

Answer 9

• benzene + haloalkane + AlCl3

Question 10

Acylation reaction w/ benzene

Answer 10

• acyl chloride + benzene + AlCl3

* product = aromatic ketone

Question 11

Compare reactivity of alkenes and bromine

Answer 11

• B = pi bonds = delocalised ∴ lower electron density
• A = pi bonds = localised around 2 carbons ∴ higher e density
• B = polarises Br2 less -the more E required

Question 12

Why is phenol a weak acid?

Answer 12

Non-polar benzene ring = partially dissociates -> phenoxide ion + proton

Question 13

How do you distinguish between phenol and a COOH

Answer 13

Only COOH will react w/Na2CO3

Question 14

Phenol + NaOH

Answer 14

Sodium phenoxide salt + H2O

Question 15

Bromination of phenol

Answer 15

White precipitate of 2,4,6-tribromophenol + HBr
Solution orange -> colourless
RTP

Question 16

Nitration of phenol (dilute HNO3)

Answer 16

Mixture of 2-nitrophenol and 4-nitrophenol is produce + H2O

RTP

Question 17

Why does phenol only need dilute acid to react compared to benzene?

Answer 17

Lone pair of electrons from the O p-orbital of -OH = delocalised into the pi system -> electron density of ring increases = attracts electrophiles more strongly + more susceptible to attack + able to polarise bromine molecules more easily

Question 18

What does delocalised e lead to?

Answer 18

Stability

Question 19

How to make an aromatic amine

Answer 19

Nitrobenzene + 6[H] + Sn/c.HCl + reflux -> ammonium salt

+ NaOH -> amine

Question 20

Compare acidity of alcohol, phenols and COOH

Answer 20

Ethanol = weakest + doesn’t react with any strong/weak base
Phenol = only reacts w/strong bases
COOH = strong enough to react with all bases

Question 21

Name the 2,4 activating groups

Answer 21

1) NH2/NHR
2) OH
3) OR
4) R

5) halogens have 2,4 directing but are not activating groups

Question 22

Why are many reactions different between alcohol and phenols

Answer 22

Because the proximity of the delocalised ring influences the OH group

Question 23

Why is an acyl chloride used to make an Ester with phenol?

Answer 23

Carboxylic acid is reactive enough to form esters w/ phenol