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

Addition Rx Mechanism (electron density diagram)

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

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

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

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 C 6 H 6,, a delocalized, conjugated  system Coplanar structure Following shows resonance stabilized Benzene structure

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

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

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

Substitution reaction of Aromatics Nitration – A ring hydrogen gets substituted with an -NO 2 group Sulfonation- A ring hydrogen is substituted with a –SO 3 H group Halogenation – A ring hydrogen is substituted with a halogen (Cl, Br, I)

Practice questions