Peroxide effect

Kharasch called this the peroxide effect and demonstrated that it could occur even if peroxides were not deliberately added to the reaction mixture Unless alkenes are pro tected from atmospheric oxygen they become contaminated with small amounts of alkyl hydroperoxides compounds of the type ROOH These alkyl hydroperoxides act m the same way as deliberately added peroxides promoting addition m the direction opposite to that predicted by Markovmkov s rule... 

The bond highlighted m yellow is the peptide bond ) Pencyclic reaction (Section 10 12) A reaction that proceeds through a cyclic transition state Period (Section 1 1) A honzontal row of the penodic table Peroxide (Section 6 8) A compound of the type ROOR Peroxide effect (Section 6 8) Reversal of regioselectivity oh served m the addition of hydrogen bromide to alkenes brought about by the presence of peroxides m the reaction mixture... 

Peroxide effect (Section 6.8) Reversal of regioselectivity observed in the addition of hydrogen bromide to alkenes brought about by the presence of peroxides in the reaction mixture. 

Cyclobutanone annulation onto a carbonyl group translates into y-butyrolactone annulation because of the facility of the Baeyer-Villiger reaction (Eq. 68 a)8). Indeed, the reaction proceeds sufficiently rapidly that even basic hydrogen peroxide effects the oxidation whereas, with less reactive carbonyl partners, peracids must be used. 

Selected entries from Methods in Enzymology [vol, page(s)] Additive properties of polarization, 246, 286 angle-resolved, assessment of peroxidation effects on membranes, 233, 274-275, 281-283, 287-288 binding isotherm construction, 246, 287-288 effect of inner filter effects, 246, 288 incoherent systems, 246, 263-264 orientational averaging, 246, 265, 269-270 Perrin equation, 246, 284-285 polarization of emission, 246, 284 rotational diffusion, 246, 9, 260 time-resolved, assessment of peroxidation effects on membranes, 233, 274, 283-285, 285-287. 

THE PEROXIDE EFFECT. FREE RADICAL ADDITION OF HBr TO ALKENES... 

Free radical addition of HBr to alkenes peroxide effect Preparation of alkyl halides... 

Propagation The bromine radical is electron deficient and electrophilic. The radical adds to the double bond, generating a carbon-centred radical. This radical abstracts hydrogen from HBr, giving the product and another bromine radical. The orientation of this reaction is anfi-Markovnikov. The reversal of regiochemistry through the use of peroxides is called the peroxide effect. 

The peroxide effect is also observed with the addition of HBr to alkynes. Peroxides (ROOR) generate anh-Markovnikov products, e.g. 1-butyne reacts with HBr in the presence of peroxide to form 1-bromobutene. 

In alkaline solution hydrogen peroxide effects oxidation to sulphate, dithionate being a probable intermediate product sulphate is also... 

Dithionic acid solutions are remarkably resistant to oxidation the cold solutions withstand the attack of hypochlorite, hypobromite and permanganic acid, although on boiling, these reagents become reduced by the sulphur dioxide liberated in the decomposition of the dithionic acid sodium peroxide effects a partial oxidation in the cold.2... 

Irradiation of olefins and dienes in the presence of oxygen and various sensitizers produces hydroperoxides and cyclic peroxides. Effective sensitizers include not only high-energy carbonyl triplets, but also low-energy organic dyes such as methylene blue, rose bengal, chlorophyl, and riboflavin. The same species that quench the phosphorescence of these complex molecules also quench their photosensitizing ability. 

MARKOWNIKOEE RULE. When a halogen acid adds to an asymmetrical etltylniic compound, the halogen usually appears on the carbon atom carrying the smaller number of hydrogen atoms this order or addition is frequently reversed with hydrogen bromide if peroxides are present (peroxide effect 1. 

N. Isenberg and M. Grdinic, A Modern Look at Markovnikov s Rule and the Peroxide Effect," J. Chem. Educ. 46, 601 (1969). 

Walling, C. and Goosen, A., Mechanism of the ferric ion catalyzed decomposition of hydrogen peroxide effect of organic substrates, /. Amer. Chem. Soc., 95(9), 2987-2991, 1973. 

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