Phenols

Question 1

What is a phenol structure?

Answer 1

an aromatic benzene ring with an -OH group attached directly

Question 2

What state is phenol at room temp?

Answer 2

solid

Question 3

Why is phenol solid at room temp unlike liquid alcohols?

Answer 3

phenol is a bigger molecule with a bigger contact surface area so it has more london forces that need to be broken to melt it

Question 4

Why is phenol only slightly soluble?

Answer 4

has an -OH group which can form H bonds with water
but it has a much larger non-polar hydrocarbon part which cannot form H bonds
the H bonding effect is outweighed by the hydrophobic aromatic ring

Question 5

What is the acidity of phenol like?

Answer 5

a very weak acidity - only a small proportion is ionised

Question 6

What is phenols molecular formula?

Answer 6

C6H5OH

Question 7

why is phenol more acidic than water and ethanol?

Answer 7

when H+ dissociates from an acid, it leaves behind a negative ion = the more stable this ion is the more favourable the dissociation will be (more acidic)

the (-) of the phenoxide ion is spread out in the pi system making the ion more stable

Question 8

Do phenols react better with strong or weak bases?

Answer 8

strong bases like -OH

Question 9

What is the reaction of phenol with NaOH?

Answer 9

C6H5OH + NaOH —-> C6H5O(-) Na(+) + H2O

Question 10

what type of structure does C6H5O(-) Na(+) have?

Answer 10

ionic - simple molecular

Question 11

What 2 weak base ions does phenol NOT react with?

Answer 11

carbonate - CO3 (2-)
hydrogen carbonate ions - HCO3 (-)

Question 12

What test is used to distinguish between a phenol or carboxylic acid?

Answer 12

reacting with carbonate or hydrogen carbonate ions
phenol = will not react
carboxylic acid = fizzing

Question 13

What test is used to distinguish between a phenol or carboxylic acid?

Answer 13

reacting with carbonate or hydrogen carbonate ions
phenol = will not react
carboxylic acid = fizzing - CO2 produced

Question 14

Why does phenol undergo electrophilic substitution more easily than benzene?

Answer 14

the ring in phenol is said to be activated by the -OH group because:

a lone pair of electrons on oxygen is delocalised into the pi system of the ring = increases electron density in the aromatic ring, making it more attractive to an electrophile
The OH is said to be an electron donating group

Question 15

Where is electron density increased the most on phenol?

Answer 15

the 2, 4 and 6 positions

Question 16

What is observed when phenol reacts with bromine?

Answer 16

bromine is decolourised
white precipitate - 2,4,6 - tribromophenol

Question 17

What are the 2 electron-donating groups?

Answer 17

-OH and -NH2

Question 18

How do electron-donating groups affect electrophilic substitution?

Answer 18

increase reactivity of the ring = higher electron density so ring is more attractive to an electrophile
they direct substitution reactions to take place at the 2,4 and 6 positions

Question 19

What is an electron-withdrawing group?

Answer 19

a group of atoms attached to the benzene ring which decreases the electron density in an aromatic ring to which it is bonded

Question 20

What is an example of an electron-withdrawing group?

Answer 20

-NO2

Question 21

What effects do electron-withdrawing groups have on electrophilic substitution?

Answer 21

decrease the reactivity of the ring = lower electron density = less atrracted to electrophile
if strongly deactivating like -NO2, they direct substitution reactions to take place at the 3 position
reaction must take place with a halogen carrier catalyst

Question 22

What is the pH of phenol roughly?

Answer 22

pH 5-6 = weak acid

Question 23

What is deduced from the reaction of phenol with NaOH?

Answer 23

phenol acts as an acid by donating a H+ to the NaOH therefore it is a weak acid

Question 24

What is deduced about phenol from reacting it with DILUTE nitric acid?

Answer 24

dilute = more reactive as benzene, does not require a fume cupboard like benzene
doesnt require an acid catalyst for nitration so phenol is more reactive

Question 25

How would you test if an alkene or phenol is present?

Answer 25

add HNO3 as alkenes do not react and phenols form an orange precipitate

Question 26

Why is phenol more reactive than benzene?

Answer 26

the p-orbitals on the oxygen atom in the phenoxide ion become delocalised in the pi-electron system in the benzene ring. This increases electron density of the delocalised pi-system making it more attractive to electrophiles and polarising electrophiles

Question 27

What are all the reactions with phenol you need to know with naming the products?

Answer 27

Br2 (aq) = 2,4,6-tribromophenol
NaOH = sodium phenoxide and water
dilute nitric acid = nitrophenol (2 products 1st or 4th position = 1st position is major product)
strong base reactions
carbonates (weak bases = no reaction