Arenes

Question 1

What is the reagent and condition for the electrophilic substituion of Halogens?

Answer 1

• X₂ anhydrous AlX₃ as catalyst at room temperature
• X₂ anhydrous FeX₃ as catalyst at room temperature

Generation of electrophile:
AlBr3 + Br-Br <=> AlBr4- + Br+
FeBr3 + Br-Br <=> FeBr4- + Br+

Question 2

What is the mechanism for the electrophilic substitution reactions?

Answer 2

Question 3

Describe the structure of benzene

Answer 3

• Each carbon atom is sp² hybridised. It forms 3 coplanar covalent bonds and remainder electron is in a 2p orbital perpendicular to the plane of atoms
• Each p orbital OVERLAPS EQUALLY with each of its neighbours resulting in six p electrons completely DELOCALISED in a 2-lobed cloud over and and under the ring of carbon atoms`
• EXTENSIVE π ELECTRON DELOCALISATION GIVES BENZENE RESONANCE STABILISATION

Question 4

What is the reagent and condition for nitration of benzene

Answer 4

Concentrated HNO₃ and concentrated H₂SO₄, heat to about 50°C to 60°C

Generation of electrophile +NO₂:

HNO₃ + 2H₂SO₄ <=> ⁺NO₂ + 2HSO₄ ^- + H₃O⁺

Question 5

What is the reagent and condition for Friedel-Crafts Alkylation

Answer 5

Reagent and Conditions: R-CH2Cl, anhydrous AlCl3 as catalyst at room temperature

Generation of electrophile:
AlCl3 + RCH2-Cl <=> AlCl4- + RCH2+

Question 6

What is the reagent and condition for side chain oxidation of alkylbenzene

Answer 6

alkylbenzne + [O] —> Benzoic acid + H2O

Reagent and conditions: KMnO4 (aq) dil H2SO4 heat

(Reaction requires at least 1 C-H bond at the position next to the benzene ring)