Phenol Flashcards
What is a phenol?
Contain a OH group bonded directly to a benzene ring
Bond angles and shapes in phenol
120 degrees in benzene ring (each carbon forms 3 bonds) so trigonal planar
104.5 degrees in O-H bond, oxygen has 2 lone pairs of electrons and forms 2 bonds so bent
Pi system in benzene ring of phenol
Each C atom is bonded to 2 C atoms and one H atom by
single covalent σ-bonds
Leaves one unused electron on each C atom in a p orbital, perpendicular to the plane of the ring.
The Six p electrons are delocalised in a ring structure above and below the plane of carbon atoms
What happens to lone pair of electrons in oxygen? (NOT DISSOCIATION)
Delocalised into the benzene ring due to overlap between:
pi bond perpendicular to plane in oxygen
ring of delocalised electrons in benzene
Above and below the plane of benzene
Why do phenols attract electrophiles more than benzene
Because lone pair of electrons in oxygen delocalised into pi system, this increases electron density above and below plan (higher electron density than benzene)
So attracts electron pair acceptors MORE
Why can phenols dissociate?
Because the lone pair of electrons on the oxygen atom are withdrawn into pi system due to overlap of p orbitals of oxygen atom with pi system
Which withdraws electron density in O-Hbond making it weaker and easier to break
What do phenols dissociate into?
Phenoxide anion
H+
Phenoxide anion
Benzene ring bonded to an oxygen anion because the O-H bond broke so electrons in this bonded was donated to oxygen atom
= -1 charged
How can phenols act as weak acids?
Because they dissociate so O-H bond breaks and the H+ ion can be donated
= acts as acid
What does the OH group do in phenol?
Activates the benzene ring
Does phenol require a halogen carrier catalyst to react with halogen?
No because unlike benzene, it has more attraction to electrophile
Is phenol soluble in water?
A small bit in cold water because despite having OH group that can form H bonds to water, non polar aromatic ring interferes with H bonding
Halogenation of phenol example
Phenol+ bromine water makes 2,4,6-tribromophenol
2,4,6-tribromophenol appearance
White precipitate that is insoluble in water
Observation for phenol+ bromine water
Forms a white precipitate + decolourises orange bromine water to colourless
Can halogenation of phenol happen with chlorine?
Yes
Conditions for halogenation of phenol
At standard room temperature and pressure
Why does phenol only require standard conditions + no catalyst needed for halogenation?
Because OH group activates the ring to attract electrophiles more strongly so hs a lower activation energy for reaction to occur
Phenol + concentrated nitric acid products
2,4,6-trinitrophenol
Can Phenol + concentrated nitric acid occur at standard conditions? WHy?
Yes because the OH group activates BENZENE RING to attract electrophiles (NO2+) more strongly
Can phenol react with dilute nitric acid?
Yes to give 2-nitrophenol and 4-nitrophenol
Why can phenol react with dilute nitric acid?
Because the OH group activates BENZENE RING to attract electrophiles (NO2+) more strongly
Are phenols weaker acids than carboxylic acids?
Yes
Can phenol react with hydroxide base?
Yes to give phenoxide salt (phenoxide anion- metal cation+)
And water
Can phenol react with metal?
Yes to give phenoxide salt (phenoxide anion- metal cation+)
AND HYDROGEN GAS
Is phenoxide salt soluble?
Yes more so than phenol so will dissolve on addition of hydroxide solution
Forms ion dipole interactions with water which is stronger than H bonds
How to differentiate phenol from carboxylic acid
React with sodium carbonate:
Phenol does not react to give negative result
Carboxylic acid gives pos result by forming effervescence which when bubbled through lime water turns cloudy
Can phenol react with a metal carbonate base?
No, not strong enough of an acid
