Phenols

Question 1

Phenol + Na:-

Answer 1

Phenol salt (phenoxide) and H2 (g)

Question 2

Phenol + NaOH:-

Answer 2

Phenoxide + H2O

Question 3

Phenol + Na2CO3:-

Answer 3

Phenol too weak, no reactt

Question 4

Phenol relative to alcohols and carboxylic acids:-

Answer 4

Less acidic than carboxylic acids, more than alcohols.

Question 5

Phenol structure:-

Answer 5

Benzene ring w/ OH group

Question 6

Why is phenol a weak acid?

Answer 6

The negative charge on the phenoxide ion is delocalised into the ring’s pi-system. Therefore, the phenoxide ion is stabilised. Consequently, phenol is a weak acid.

Question 7

Phenoxide ion:-

Answer 7

Benzene ring with O^- branch.

Question 8

Acid acidity level:-

Answer 8

Determined by stability of ion when H+ is lost. The more the negative charge can be delocalised, the more stable the ion.

Question 9

Phenol use:-

Answer 9

Mainly used as disinfectants.

Question 10

Phenol at room temp:-

Answer 10

Solid at room temp as is bigger molecule than ethanol w/ a bigger surface contact area = more induced dipole-dipole forces need to be broken to melt it.

Question 11

Phenol water solubility:-

Answer 11

Only slightly soluble in water (compared to freely soluble ethanol). Phenol has a much larger non-polar hydrocarbon part which cannot form hydrogen bonds.

Question 12

Why does phenol undergo electrophilic sub reactions much more easily than benzene?

Answer 12

The ring is “activated” by the -OH group, no catalyst needed.

Question 13

Ring = activated:-

Answer 13

Lone pair of electrons delocalised into pi-system, increasing electron density and making it more attractive to an electrophile
The -OH is therefore said to be an electron donating group.

Question 14

2,4,6 substitution:-

Answer 14

The electron density is increased most at these positions so this where substitution normally occurs e.g:-
Phenol + 3Br2 -> 2,4,6-tribromophenol + 3HBr.
White precipitate and bromine decolourised.

Question 15

Benzene + Br vs Phenol+ Br:-

Answer 15

No solvent for Benz, water for Phenol.
Halogen carrier catalyst for Benz, none for Phenol.
1 H atom easily replaced for Benz, 3 for Phenol.

Question 16

Blocking substitution:-

Answer 16

Only H on aromatic ring can normally be replaced i.e if another group is at 2,4 or 6, substitution will not happen there.

Question 17

Electron-donating groups:-

Answer 17

-OH and -NH2 are edgs when bonded to aromatic ring bc the O in (in -OH) or N (in -NH2) has a lone pair which can delocalise into pi-system of ring, increasing electron density.

Question 18

2 important effects of EDGs on electrophilic sub reactions:-

Answer 18

• increase ring reactivity bc higher electron density makes ring more attractive to an electrophile.
• direct sub reactions to take place at 2,4,6 positions unless blocking occurs.

Question 19

Electron withdrawing groups:-

Answer 19

-NO2 is an EWG, which decreases electron density in aromatic ring it’s bonded to.

Question 20

2 EWG effects on electrophilic sub reactions:-

Answer 20

• decrease ring reactivity as lower electron density = less reactive to an electrophile.
• if they are strongly deactivating, they direct sub reactions to take place at the 3 position, provided it isn’t blocked.