M6 Knowledge gaps

Question 1

Kekulé and Benzene: similarities/differences

Answer 1

Similarities: π-bonds formed from sideways overlap of adjacent p-orbitals above and below plane of molecule, molecular formula of C6H6
Kekulé: 3 localised π-bonds and 3 single C-C bonds
Benzene: delocalised π-ring system by p-orbital overlap in both directions, more stable

Question 2

Experimental evidence for benzene

Answer 2

X-ray diffraction shows all C-C bond lengths are equal
Does not decolourise bromine water
Enthalpy of hydrogenation is less exothermic than expected

Question 3

Freidel-Crafts reaction conditions

Answer 3

• anhydrous
• halogen carrier catalyst
• reflux

Question 4

2,4-directing groups

Answer 4

-OH
-NH2
-R

Question 5

3-directing groups

Answer 5

-NO2
-COOH
-COR

Question 6

Why are amines basic?

Answer 6

Lone pair on nitrogen accepts a proton

Question 7

Purification by recrystallisation

Answer 7

Dissolve in min. volume hot solvent
Filter insoluble impurities then leave to cool and crystallise
Filter again to remove soluble impurities
Wash with cool solvent and leave to dry

Question 8

Purification by redistillation

Answer 8

Neutralise acid with NaOH/KOH (where applicable)
Remove immiscible aqueous layer from separating funnel
Add drying salt (e.g., MgSO4) and filter
Distil and collect fraction at [melting point]