Chapter 25.3/4 Aromatic compounds

Question 1

What are phenols?

Answer 1

Organic chemicals that contain a hydroxyl OH group functional group directly bonded to an aromatic ring

C6H5OH = phenol
–> NOT alcohol

Question 2

Phenol as a weak acid: solubility in water

Answer 2

Phenol is less soluble in water than alcohols due to the NON-POLAR benzene ring
–> partially dissociates in water, forming phenoxide ion and proton (C6H5O- + H+)

Question 3

Phenol as a weak acid: acidity

Answer 3

phenol= more acidic than alcohols but less acidic than carboxylic acids
–> found by comparing Ka (acid dissociation constant)

Question 4

Phenol as a weak acid: test for differentiating between phenol and carboxylic acid

Answer 4

Reaction with Sodium carbonate as:
- ethanol does not react with sodium hydroxide NaOH (strong base) or sodium carbonate Na2CO3 (weak base)

• Phenols and carboxylic acids react with strong bases
  -ONLY carboxylic acids can react with weak bases like Na2CO3

Question 5

Phenol reacting with NaOH

Answer 5

C6H5OH + NaOH –> C6H5Na+O- + H2O

neutralisation: forms salt ( sodium phenoxide) and water

Question 6

Reactivity of phenol vs benzene

Answer 6

OH functional group makes phenols more reactive than benzene
- oxygen brings lone pair which can become PARTIALLY DELOCALISED into the ring, making it more electron dense
- increased electron density attracts electrophiles more strongly

=> aromatic ring of phenol is more susceptible to attack from electrophiles than benzene

Question 7

Bromination of phenol: standard reaction

Answer 7

Phenol reacts with aqueous solution of bromine to form white precipitate of 2,4,6-tribbromophenol
- reaction decolorises bromine water (orange to colourless)

• halogen carrier is not needed (phenol more reactive than benzene) and room temperature

Question 8

Bromination of phenol: equaiton

Answer 8

C6H5OH + 3Br2 –> C6H2Br3OH + 3HBr

Question 9

nitration of phenol

Answer 9

Phenol reacts readily with DILUTE nitric acid at room temp (no catalyst)
- forms either 2-nitrophenol or 4-nitrophenol

Question 10

What are activating groups? name all examples

Answer 10

Groups that increase the reactivity of benzene ring aka electron donating groups

Includes: NH2, NHR, OH, OR, R

Question 11

What are deactivating groups? name all examples

Answer 11

Groups that decrease the reactivity of benzene ring aka electron withdrawing groups

Includes: COR (carbonyl) , COOR, SO3H, CHO (aldehyde), COOH, CN (nitrite), NO2, NR3+, Halogens
–> all of these have double/ triple bonds and also contain permanent dipoles due to large difference in electronegativity)

Question 12

What happens due to activating groups?

Answer 12

Reactions will be faster / require lower temperatures/ need more mild conditions in relation to benzene itself

Question 13

What happens due to deactivating groups?

Answer 13

Reactions will be slower/ require higher temperatures/ need more harsh conditions in relation to benzene

Question 14

What are Ortho/para directing groups?

Answer 14

Groups force an additional group to substitute onto ortho (2nd carbon) and para (4 carbon) on benzene ring
includes: NH2, NHR,OH,OR,R or C6H5 or HALOGENS

Question 15

How does ortho/para groups affect the benzene ring?

Answer 15

These groups donate electrons onto ring
- increases reactivity of ring (except when halogens attach)
- 2nd stabilisation at ortho or para position

Question 16

What are meta directing groups?

Answer 16

Groups that force additional group to substitute onto meta (3rd carbon) position on benzene ring
Includes: COR,COOR,SO3H,CHO,COOH,CN,NO2, NR3+

Question 17

How do meta groups affect the benzene ring?

Answer 17

Groups withdraw electrons from ring
- reducing reactivity
- 2nd stabilisation occurs at meta position