Mechanism of addition of HBr to an Alkene

1. Mechanism of addition of HBr to an Alkene Step 1: Formation of a carbocation Step 2: Nucleophillic addition of bromide

2. Addition Rx Mechanism(electron density diagram)

3. Alkene Polymerization • Polymerization of alkenes is an industrially important reaction • Plastics such as polypropylene and polyethylene are products of alkene polymerization • Alkene polymerization takes place in presence of catalysts • Refer to Table 13.1 of textbook for some important alkene monomers and their polymers

4. Addition of Halogens: Halogenation Halogens add to alkenes to form 1,2-dihaloalkanes Fundamentals of General, Organic and Biological Chemistry, Prentice-Hall, McMurry et.al, 5ed

5. Alkenes & their Polymers Fundamentals of General, Organic and Biological Chemistry, Prentice-Hall, McMurry et.al, 5ed

6. Aromatic Compounds • The term ‘aromatic’ originated from compunds that had a fragrant smell and were isolated from nature • Aromatic compounds have an arrangement of alternating double and single bonds, i.e C6H6, , a delocalized, conjugated p system • Coplanar structure • Following shows resonance stabilized Benzene structure

7. Benzene • Benzene lacks reactivity due to its resonance stabilization • Benzene does not undergo any addition reactions Fundamentals of General, Organic and Biological Chemistry, Prentice-Hall, McMurry et.al, 5ed

8. Naming Aromatic Compounds Fundamentals of General, Organic and Biological Chemistry, Prentice-Hall, McMurry et.al, 5ed

9. Nomenclature of Aromatics • The cyclic aromatic ring is treated as the parent chain compound • The parent compound has accepted names such as indole, furan, phenol being accepted in the IUPAC nomenclature

10. Substitution reaction of Aromatics • Nitration – A ring hydrogen gets substituted with an -NO2 group • Sulfonation- A ring hydrogen is substituted with a –SO3H group • Halogenation – A ring hydrogen is substituted with a halogen (Cl, Br, I)

11. Practice questions