Markovnikov rule

The attack of OH obeys the Markovnikov rule. Higher alkenes are oxidized to ketones and this unique oxidation of alkenes has extensive synthetic appli-cations[23]. The oxidation of propylene affords acetone. Propionaldehyde is... 

Regioselectivity of Hydrogen Halide Addition Markovnikovs Rule... 

Markovnikovs rule (Section 6 5) An unsymmetrical reagent adds to an unsymmetncal double bond in the direction that places the positive part of the reagent on the carbon of the double bond that has the greater number of hydrogens... 

The reaction first occurs between Cj and H with the largest amplitudes of the frontier orbitals, in agreement with the Markovnikov rule. 

In accord with the Markovnikov rule, the hydroxy group is introduced at the carbon best able to support positive charge. 

Acid-catalyzed additions to terminal alkynes follow the Markovnikov rule. 

The most synthetically valuable method for converting alkynes to ketones is by mercuric ion-catalyzed hydration. Terminal alkynes give methyl ketones, in accordance with the Markovnikov rule. Internal alkynes give mixtures of ketones unless some structural feature promotes regioselectivity. Reactions with Hg(OAc)2 in other nucleophilic solvents such as acetic acid or methanol proceed to (3-acetoxy- or (3-methoxyalkenylmercury intermediates,152 which can be reduced or solvolyzed to ketones. The regiochemistry is indicative of a mercurinium ion intermediate that is opened by nucleophilic attack at the more positive carbon, that is, the additions follow the Markovnikov rule. Scheme 4.8 gives some examples of alkyne hydration reactions. 

Examination of the HOMO and LUMO orbitals in these TSs indicates that the electronic effect operates mainly through the LUMO. The EWG cyano tends to localize the LUMO on the (3-carbon, whereas ERG substituents have the opposite effect. Similar trends were found for Pd coordinated by diimine ligands.150 These results indicate that the Markovnikov rule applies with the more electrophilic Pd complexes. When steric effects become dominant, the Pd adds to the less hindered position. 

The hydration of an alkene double bond under strongly acidic conditions is again a classical reaction that involves a carbocation intermediate, which often leads to various competing reaction products.27 The regiochemistry of the water addition follows the Markovnikov rule.28... 

Addition takes place selectively when the reaction is carried out in methanol by using the redox couple of Br /Br+ as the mediator as shown by some typical examples in Table 36. The mechanism of this 1,2-addition may be as shown in equation 3 on the basis that it is regio- and stereoselective and follows the Markovnikov rule. 

Markovnikov rule, 20 774 Markov property, 26 1022 Markush chemical structures, indexing and searching, 18 242. See also WPI entries... 

The modern Markovnikov rule states that, in the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent adds to a carbon atom of the double bond to yield the more stable carbocation as an intermediate. Thus, Markovnikov addition to unsymmetrical n bonds produces regioselective product. 

When halogenation of alkenes is carried out in aqueous solvent, a vicinal halohydrm is obtained. The reaction is regioselective, and follows the Markovnikov rule. The halide adds to the less substituted carbon atom via a bridged halonium ion intermediate, and the hydroxyl adds to the more substituted carbon atom. The reaction mechanism is similar to the halogenation of alkenes, except that instead of the halide nucleophile, the water attacks as a nucleophile. 

Additions to carbon-carbon multiple bonds initiated by electrophiles are generally governed by the Markovnikov rule. However, the rule must be modified to accom-ipodate such substrates as vinylsilanes. The so-called anti-Markovnikov hydro-halogenation [105] is to be contrasted to the Markovnikov addition for allylsilanes. In fact, when one recognizes the acceptor role of the silicon atom and applying the polarity alternation rule, the puzzling results become self-consistent. 

The addition of water and methanol to terminal alkynes has also been studied by Laguna et al. by pentafluorophenyl and mesityl gold derivatives. Both acidic and non-acidic conditions led to high activity, even in the presence of as little as 0.5 mol% of catalyst. The use of pentafluorophenyl compounds allowed them to obtain additional spectroscopic information in the stoichiometric reaction of the complex [Au (C6F5)2C1]2 and phenylacetylene, which showed that gold(III) was the active species in the catalytic process. The reaction followed the Markovnikov rule, as shown in the proposed mechanism (Scheme 8.13), delivering the corresponding ketones or diacetal products [96]. 

The addition is regiospecifie according to the Markovnikov rule, thus oct-l-ene (12) reacts with xenon difluoride and diphenyldiselenide to form 2-fluoro-l-(phenylseleno)octane (13) in 63% yield and 2-hydroxy-l-(phenylseleno)octane (14) in 8% yield.51,52... 

Bromine monofluoride or iodine monofluoride can be prepared from the corresponding elements in trichlorofluoromethane at — 781 and — 45 C,2,3 respectively. The compounds are unstable and decompose at low temperatures, iodine monofluoridc at — 14 C2,3 and bromine monofluoride, in part, even at — 78 C.1 Therefore, they are used, without separation and purification, in Freon solutions at low temperatures or, most frequently, as stoichiometric mixtures bromine trifluoride/bromine and iodine pentafluoride/iodine. A solution of iodine monofluoride, obtained by bubbling nitrogen-diluted fluorine gas into a suspension of iodine in trichlorofluoromethane at — 75 C, was used for addition to alkene C = C bonds. The reaction is regioselective and in most cases obeys the Markovnikov rule.4 Iodine monofiuoride prepared in situ reacts quite efficiently with steroidal alkenes.4... 

Addition reactions to the C = C bond arc observed in reactions of perchloryl fluoride in methanol in the presence of potassium carbonate at 15 C, when protected prostacyclins are fluorinated. Fluorine enters the molecule according to the Markovnikov rule and the formation of four isomers has been established.34... 

The reaction of alkenes 2 in the presence of a nucleophilic species (hydrogen fluoride, methanol, acetic acid) gives vicinal difluorides, methoxy fluorides or acctoxy fluorides in high yield fluorine enters according to the Markovnikov rule.8... 

Hydration is regioselective and follows the Markovnikov rule. The involvement of carbocationic intermediate can result in rearrangements. 

Exceptions to the Markovnikov rule when hydrogen bromide reacts with unsym-metric alkenes have long been known.117,118 The reaction for this anti-Markovnikov addition was explained as being a chain reaction with the involvement of bromine atoms influenced by the presence of peroxides.119-121 Both added peroxides and peroxides formed by the action of oxygen (air) on the alkene are effective. 

It is significant that no other hydrogen halides add to alkenes, contrary to the Markovnikov rule, even in the presence of free radicals. This appears to be due to the difficulty with which other halogen atoms, particularly fluorine and chlorine, are produced by reaction of the hydrogen halides with radicals ... 

In accordance with the Markovnikov rule, terminal alkynes are converted to 2-halo-l-alkenes. The reagents prepared in the reaction of anhydrous HF with organic bases and used in hydrofluorination of alkenes can add to the carbon-carbon triple bond producing Markovnikov products.94-96,98 99 However, 1-bromo-l-alkenes and... 

Substituted acetylenes react more slowly than does acetylene. The Markovnikov rule is usually followed, that is, terminal acetylenes form 2-substituted acrylic acids122,124,161 [Eq. (7.19)162] ... 

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