Chapter 25.3/4 Aromatic compounds Flashcards

25.3 Chemistry of phenol 25.4 Directing groups

1
Q

What are phenols?

A

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

C6H5OH = phenol
–> NOT alcohol

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2
Q

Phenol as a weak acid: solubility in water

A

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+)

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3
Q

Phenol as a weak acid: acidity

A

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

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4
Q

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

A

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
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5
Q

Phenol reacting with NaOH

A

C6H5OH + NaOH –> C6H5Na+O- + H2O

neutralisation: forms salt ( sodium phenoxide) and water

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6
Q

Reactivity of phenol vs benzene

A

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

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7
Q

Bromination of phenol: standard reaction

A

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
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8
Q

Bromination of phenol: equaiton

A

C6H5OH + 3Br2 –> C6H2Br3OH + 3HBr

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9
Q

nitration of phenol

A

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

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10
Q

What are activating groups? name all examples

A

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

Includes: NH2, NHR, OH, OR, R

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11
Q

What are deactivating groups? name all examples

A

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)

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12
Q

What happens due to activating groups?

A

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

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13
Q

What happens due to deactivating groups?

A

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

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14
Q

What are Ortho/para directing groups?

A

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

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15
Q

How does ortho/para groups affect the benzene ring?

A

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

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16
Q

What are meta directing groups?

A

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

17
Q

How do meta groups affect the benzene ring?

A

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