25.3,4 - Phenols & Directing Groups

Question 1

What is phenol?

Answer 1

• Contains a hydroxyl on the aromatic ring
• Hydroxyl must be directly attached to the ring, not on a side chain, otherwise it is an alcohol

Question 2

Why is phenol classed as a weak acid?

Answer 2

• Phenol, less soluble in H₂O(l) than alcohols due to non-polar benzene ring.
• When phenol dissolves in water it partially dissociates to form a phenoxide ion and a proton (H⁺)

Question 3

Compare the acidity of alcohols, phenols & carboxylic acids.

Answer 3

ACIDITY
carboxylic acids > phenols > alcohols

Carboxylic acids react with strong bases (NaOH) and weak bases (Na₂CO₃)

Phenol reacts with NaOH not sodium carbonate

Alcohols react with neither

Question 4

What happens when phenol reacts with NaOH?

Answer 4

Forms sodium phenoxide + water

Question 5

What is the difference between the bromination of benzene and phenol?

Answer 5

Phenol: Doesn’t requre halogen carrier catalyst and works at room temperature

White precipitate forms

C₆H₅OH + 3Br₂ → 2,4,6 - tribromophenol + 3HBr

Question 6

What is the difference between the nitration of phenol and benzene?

Answer 6

Readily reacts w/ dilute HNO₃ at RT

Forms 2 and 4-nitrophenol

Question 7

Compare the reactivity of phenol with benzene.

Answer 7

Phenol is more reactive

• Lone pair of O on p-orbital of hydroxyl is donated to pi-systemo of phenol, increasing electron density
• Benzene can’t induce dipoles (e.g. to Br₂), phenol & cyclohexane can
• Phenol is now more susceptible to an electrophile attack

Question 8

What is activation/deactivation?

Answer 8

• Some substituent groups activate the aromatic ring to react more readily with electrophiles
• Some substituent groups deactivate (doing the opposite of activating)
• Activating & deactivating groups direct secondary substituent groups

Question 9

What are the different directing groups?

Answer 9

2-, 4- directing (ACTIVATING/ ELECTRON DONATING)

• NH₂, -NHR
• OH, -OR
• R, -C₆H₅

{-F, -Cl, -Br, -I} not activating

3-directing (DEACTIVATING, ELECTRON WITHDRAWING)

-RCOR, -COOR, -SO₃H, -CHO, -COOH, CN, -NO₂, -NR₃⁺