abdul razzaq Free radical

Seminar on Free Radicals : 

Seminar on Free Radicals Presented by:- Mr. ABDUL RAZZAQ M. Pharm Dept. of Pharma Chemistry Luqman college of pharmacy, Gulbarga

Contents… : 

Contents… Formation of Free radical Structure of Free radical Stability of Free radical Detection of Free radical Reactions involving of free radicals. Addition of carbon-carbon multiple bonds References

Slide 3: 

3 Introduction: Free radicals are atoms, molecules or ions with unpaired electrons . These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions. Free radicals are formed by Homolytic and Heterolytic fission.

Production of Free radicals : 

Production of Free radicals A] Thermal Reactions N2+ Vapours of tetramethyllead Vacuum pump Paneth technique B A

B] Photochemical Reactions : 

B] Photochemical Reactions Absorption of visible or ultraviolet light provides a molecule with sufficient energy to break covalent bonds to yield radicals

C] Redox Reactions : 

C] Redox Reactions One-electron oxidation-reduction are very often employed to produce radicals. Eg. Kolbe electrolysis of the salts of organic acids.

Detection of Radicals : 

Detection of Radicals 1] Use of radical indicator such as hydroquinone, organic peroxides. 2] Electron spin resonance (ESR) or electron paramagnetic resonance (EPR): directly measures the Paramagnetism, 3] Chemically induced dynamic nuclear polarization: NMR instrument.

Stability of Radicals : 

Stability of Radicals 1]To compare the stabilities of various radicals is to calculate the bond dissociation energy, smaller the amount of energy required for bond rupture , the more stable is the radicals. 2] Hyperconjugative Mechanism-The stability increases with the number of alkyl groups that are attached to the carbon atom carrying unpaired electron Eg. ter. butyl radical

Slide 9: 

3]Steric factor: Eg. allyl(I) and benzyl(II) radicals are stable as in this case π electrons become delocalized into the half-filled orbital.

Reactions of Radicals : 

Reactions of Radicals A] Polymerization B] Halogenation C] Addition Reaction D] Autooxidation E] Rearrangement of Radicals

A] Polymerization : 

A] Polymerization A] Initiation This consists in the decomposition of benzoyl peroxide into benzoyloxy (Phenyl) radicals & their subsequent attack on the double bond of styrene.

B] Propagation : 

B] Propagation Radical adds to the styrene double bond

C] Termination : 

C] Termination Two chains interact either by combination or by disproportionation

B] Halogenation : 

B] Halogenation Initiation : Separation of the halogen (X2) into two radicals by the U.V. light. Propogation : The first step is the abstraction of the hydrogen atom from the tertiary carbon The tertiary radical then reacts with another one of the chlorine molecules to form the product.

C] Addition ReactionsAddition of HBr to alkenes : 

15 C] Addition ReactionsAddition of HBr to alkenes

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16 D] Autooxidation (addition reaction) Perbenzoic acid reacts with a molecule of benzaldehyde to produce two molecules Of benzoic acid benzaldehyde benzoic acid

G] Rearrangement of radicals : 

G] Rearrangement of radicals β- phenylisovaleraldehyde

Addition to Carbon-Carbon Multiple bond : 

Addition to Carbon-Carbon Multiple bond It may be initiated by an electrophiles, a nucleophile, or a free radical. A] Electrophilic Additions - Effect of Substituents on the rate of additions. - Addition of Hydrogen halide: Markownikoff’s rule. - Additions to Alkynes. - Hydroboration. - Epoxidation and hydroxylation. - Ozonolysis. - Addition to Conjugated dienes. - Diels-Alder reaction. - 1,3-Dipolar addition. B] Nucleophilic Additions. - Addition to Acrylonitrile: Cyanoethylation.

Slide 19: 

Addition to Conjugated dienes The addition occurs in the direction which leads to a resonance stabilized allylic cation.

References: : 

References: 1) Jery March,,Advanced Organic Chemistry,Wiley International Publication,4th Edition 2) S.Mukharjee & S.P.Singh,Reaction Mechanisms in Organic Chemistry,3rd Edition 3) Morison & boyd, Organic Chemistry 4) I.L.Finar,Organic Chemistry Vol-1,5th Edition 5) Tietze, L. F.; Bratz, M. Org. Syn., Coll. Vol. 9, p.314 (1998); Vol. 71, p.214 (1993). 6) http://www.organic-chemistry.org/namedreactions/ozonolysis-criegee-mechanism.shtm

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Thank you