Alkenes Markovnikov’s rule

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... 

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. 

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 ... 

Let s compare the carbocation intermediates for addition of a hydrogen halide (HX) to an unsymmetrical alkene of the type RCH=CH2 (a) according to Markovnikov s rule and (b) opposite to Markovnikov s rule (a) Addition according to Markovnikov s rule... 

Acid catalyzed hydration converts alkenes to alcohols with regioselectivity according to Markovnikov s rule Frequently however one needs an alcohol having a structure that corresponds to hydration of an alkene with a regioselectivity opposite to that of Markovnikov s rule The conversion of 1 decene to 1 decanol is an example of such a transformation... 

A proton and a halogen add to the double bond of an alkene to yield an alkyl halide Addition proceeds in ac cordance with Markovnikov s rule hy drogen adds to the carbon that has the greater number of hydrogens halide to the carbon that has the fewer hydro gens... 

Alkenes react with sulfuric acid to form alkyl hydrogen sulfates A proton and a hydrogen sulfate ion add to the double bond in accordance with Markovnikov s rule Alkenes that yield tertiary carboca tions on protonation tend to polymerize in concentrated sulfuric acid (Section 6 21)... 

Hydroboration-oxidation (Sections 6 11-6 13) This two step sequence achieves hydration of alkenes in a ste reospecific syn manner with a regiose lectivity opposite to Markovnikov s rule An organoborane is formed by electro philic addition of diborane to an alkene Oxidation of the organoborane inter mediate with hydrogen peroxide com pletes the process Rearrangements do not occur... 

Acid catalyzed hydration of alkenes (Section 6 10) Water adds to the double bond in accordance with Markovnikov s rule... 

Hydroboration-oxidation of alkenes (Section 6 11) H and OF add to the double bond with a regioselectivity opposite to that of Markovnikov s rule This is a very good synthetic method addition is syn and no rearrangements are observed... 

Addition of water to the double bond of an alkene takes place in aqueous acid. Addition occurs according to Markovnikov s rule. A carbocation is an intermediate and is captured by a molecule of water acting as a nucleophile. 

Markovnikov s rule is used to predict the regiochemistry of HX (electrophilic) addition reactions. The rule states that HX adds to an unsymmetrical alkene mainly in the direction that bonds H to the less substituted alkene carbon and X to the more substituted alkene carbon. 

Use Markovnikov s rule to predict the products of HBr addition to the alkenes shown above. 

Electrophilic addition of hydrogen bromide to alkenes follows Markovnikov s rule, leading to the product with halogen on the more-substituted position. However, trace amounts of hydroperoxides (among other impurities ) may initiate a reaction that gives rise to the anti-Markovnikov product, with bromine in the less-substituted position. 

Markovnikov s rule In the addition of HX to an alkene, the H attaches to the carbon with fewer alkyl substituents and the X attaches to the carbon with more alkyl substituents. 

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