5: Phenols Flashcards
what is a phenol
An aromatic ring with an -OH directly attached
Why does phenol have a higher melting and boiling point than ethanol
Phenol is a bigger molecule, so has a larger surface area for induced dipole-dipole forces.
Why is Phenol less soluble than ethanol in water
Both have an -OH group which can form hydrogen bonds with water but phenol has a much larger non-polar part
Is phenol acidic in water
very weak acid
Equation to show how phenol is acidic
C₆H₅OH (aq) ⇌ C₆H₅O¯ (aq) + H†(aq)
Why is phenol more acidic than water or ethanol
When H† dissociates from an acid, it leaves behind a negative ion. The more stable the ion is, the more favourable the dissociation - ie the more acidic.
The negative charge on the oxygen of C₆H₅O¯ is delocalised into the pi system so it is a stable ion, more stable than a hydroxide ion (water) or ethoxide ion (ethanol).
What bases will phenol react with
Strong bases like hydroxides
What bases will phenols not react with
Weak bases like carbonates
Why can phenols undergo electrophilic substitution
The ring is activated by the -OH group
How does the -OH group activate the ring
A lone pair of electrons on oxygen is delocalised into the π system of the ring. This increases the electron density in the aromatic ring, making it more attractive to an electrophile.
What positions in the ring have a favoured substitution
2,4 and 6 as there is an increased electron density there
What are the observations of phenol + bromine
Bromine is decolourised,
White precipitate is formed
Does phenol plus bromine need a catalyst
No
What are the electron donating groups
-OH and -NH₂
What is the electron withdrawing group
-NO₂
