Alkenes Markovnikov

There is direct evidence, from IR and NMR spectra, that the re/T-butyl cation is quantitatively formed when tert-butyl chloride reacts with AICI3 in anhydrous liquid HCl. In the case of alkenes, Markovnikov s rule (p. 984) is followed. Carbocation formation is particularly easy from some reagents, because of the stability of the cations. Triphenyhnethyl chloride and 1-chloroadamantane alkylate activated... 

Addition of Hydrogen Halides to Alkene Markovnikov s Rule... 

Chlorofluorination of alkenes and alkynes using the A -chlorosaccharin-hydrogen fluoride/ pyridine system (Method G)50 results in vicinal chlorofluoro-substituted alkanes or alkenes, respectively. Since this system is more reactive than with other A -chloroamides, its use allows shorter reaction times and milder reaction conditions to prepare chlorofluorinated products in higher yields. With phenyl-substituted alkenes, Markovnikov-type adducts are formed exclusively. The additions proceed predominantly anti, with varying degrees of stereoselectivity. 

Concentrated HI in water or acetic acid is usually applied in hydroiodination of alkenes. Markovnikov products are exclusively formed and rearrangements may be observed. 

This is the original statement of Markovnikov s rule. Reactions that follow this rule are said to follow Markovnikov orientation and give the Markovnikov product. We are often interested in adding electrophiles other than proton acids to the double bonds of alkenes. Markovnikov s rule can be extended to include a wide variety of other additions, based on the addition of the electrophile in such a way as to produce the most stable carbocation. 

Regioselectivity is quite predictable, and consistent in a simple way with typical electrophilic activation of an alkene (Markovnikov s rule). Just as in bromination of an nnsymmetrical alkene, initial coordination of an electrophile (M+, Br+) activates the alkene toward nncleophilic addition of a nncleophile, the addition is preferred at the end of the alkene that best stabilizes a cation. Electronic effects dominate over steric effects. An molecnlar orbital (MO) analysis has been pnt forward ( the slip mechanism ) to rationalize the activating effect of the metal and, in a secondary way, the regioselectivity. It focnses on the reactants and prodncts, and notes that the metal moves dnring the reaction from the approximate midpoint of the alkene to one end. As that slip occurs toward one end of the alkene, the lowest unoccupied molecular orbital (LUMO) for the complex changes and a large coefficient develops at the other end. 

Improved results were achieved when trichlorosilane was treated with alkenes in the presence of a ferrocenyl-palladium catalyst, [(7 )-(5)-PPFA]PdCl2 8a. In the ease of unsymmetrica alkenes, Markovnikov addition products are formed. 

Alkene chemistry is dominated by electrophilic addition reactions. When MX reacts with an unsyinmetrically substituted alkene, Markovnikov s rule predicts that the H will add to the carbon having fewer alkyl substituents and the X group will add to the carbon having more alkyl substituents. Electrophilic additions to alkenes take place through carbocation intermediates formed by reaction of the nucleophilic alkene tt bond with electrophilic H. Carbocation stability follovvs the order... 

There is direct evidence, from ir and nmr spectra, that the fert-butyl cation is quantitatively formed when ferf-butyl chloride reacts with AICI3 in anhydrous liquid HCl. In the case of alkenes, Markovnikov s rule (p. 1019) is followed. Carbocation formation is particularly easy from some reagents, because of the stability of the cations. Triphenylmethyl chloride and 1-chloroadamantane alkylate activated aromatic rings (e.g., phenols, amines) with no catalyst or solvent. Ions as stable as this are less reactive than other carbocations and often attack only active substrates. The tropylium ion, for example, alkylates anisole, but not benzene. It was noted on p. 476 that relatively stable vinylic cations can be generated from certain vinylic compounds. These have been used to introduce vinylic groups into aryl substrates. Lewis acids, such as BF3 or AIEta, can also be used to alkylation of aromatic rings with alkene units. 

Alkenes Markovnikov s Rule Formation of the More Stable Carbocation Dienes Alkynes Allenes... 

This mechanism explains the formation of the more highly substituted alcohol from unsymmetrical alkenes (Markovnikov s rule). A number of other points must be considered in order to provide a more complete picture of the mechanism. Is the protonation step reversible Is there a discrete carbocation intermediate, or does the nucleophile become involved before proton transfer is complete Can other reactions of the carbocation, such as rearrangement, compete with capture by water ... 

Regioselectivity is quite predictable, and consistent in a simple way with typical electrophilic activation of an alkene (Markovnikov s rule). Just as in bromination of an... 

The Chemistry of Vision Addition and Substitution Reactions Compared Polar Addition Reactions Addition of Unsymmetric Reagents to Unsymmetric Alkenes Markovnikov s Rule Mechanism of Electrophilic Addition to Alkenes Markovnikov s Rule Explained Reaction Equilibrium What Makes a Reaction Go ... 

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