Markownikoff rule

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

Acid-catalyzed additions to alkynes follow the Markownikoff 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 Markownikoff rule. Internal alkynes will 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 / -acetoxy- or /i-mcthoxyalk-enylmercury intermediates.116 These intermediates can be reduced to alkenyl acetates or solvolyzed to ketones. The regiochemistry is indicative of a mercurinium ion intermediate which is opened by nucleophilic attack at the more positive carbon that is, the additions follow the Markownikoff rule. Scheme 4.7 gives some examples of alkyne addition reactions. 

The addition of HX to alkenes proceeds according to the Markownikoff rule, i.e. the halogen is attached to the more substituted carbon atom [321—323], The reactivity order of butenes was found to be dependent on the nature of the catalyst. Over MgS04, the order was isobutene > trans-2-butene > 1-butene > cis-2-butene but with CaCl2, the reactivity decreased in the order isobutene > m-2-butene > 1-butene > trans-2-butene [321], Propene is more reactive than ethylene [318], Earlier reports that tert-butylchloride is formed from 1-butene and hydrogen... 

The addition of hydrogen halides to steroidal olefins has been assumed to proceed through carbonium ion intermediates, although there is no clear evidence as to the details of the process. 3rMethyl-5a cholest-2-ene (6) [8y] and cholest-5-ene (8) [88] give the products (7) and (9), respectively, according to the "Markownikoff rule . The intermediate in each case... 

Two anomalous reactions have been reported which appear to obey the Markownikoff rule. The addition of I-F (as A/ -iodosuccinimide/HF) [g2] or I-Cl [gi] to a A -bond gave the 5a-fluoro- and 5a-chloro-6j8-iodo compounds (13a) and (13b) respectively, resulting from opening of a iodonium complex (12. The I-F reaction has been discussed... 

The hydration of alkenes (Scheme 2.10a) is a useful way of generating alcohols. In the acid-catalysed hydration of an alkene, the initial electrophilic attack by a proton affords the more stable carbenium ion (car-bocation), which is then neutralized by the attack of a water molecule. In the case of an unsymmetrical alkene this hydration follows the Markownikoff rule This rule states that the electrophilic part of the addendum becomes attached to the carbon atom that bears the greater number of hydrogen atoms. This generates the more stable, more highly substituted carbenium ion. 

Electrophilic addition to alkenes, such as the addition of hydrogen bromide under ionic conditions, follows the Markownikoff rule which states that in the addition of HX to an alkene, the hydrogen atom (the electrophile) becomes attached to the less-substituted carbon atom. The addition of halogens such as bromine proceeds via a halonium ion, and takes place with an overall trans stereochemistry. 

Electrophilic cyclization of dimethyl(o -phenylaminoalkyl)alkenylsilanes has been studied by Kirpichenko et al. <2001JGU1874>. They found that ring closure by vinyl(phenylaminomethyl)dimethylsilane 165 proceeded contrary to the Markownikoff rule (Equation 28). 

Markownikoff rule In the addition of hydrogen halides to unsymmetrically constituted (unsaturated) hydrocarbons, the halogen atom becomes attached to the carbon bearing the lesser number of hydrogen atoms. Originally formulated by Markownikoff (Markovnikov) to generalize the orientation in additions of hydrogen halides to simple alkenes, this rule... 

Markownikoff rule. When a halogen acid adds... 

The hydrogen of HCo(dp)2 and HCo(PBu3)4 can be regarded as H rather than H+. Consequently, the reactivity or catalytic activity of these complexes differs. For example, the difference in iso/normal ratio in the oxo reaction was explained in terms of the difference in the ligands 53 56T Thus, when a phosphine such as PBu3 is coordinated to cobalt, the ratio of normal increases over that obtained with the corresponding carbonyl. In this case, a straight chain is formed by the olefin insertion when the acidity of the hydride is decreased. The increase of the normal aldehydes relative to iso aldehydes can be explained by the Markownikoff rule. Of course, as in many other cases, the steric effect, in addition to the electronic effect, should be considered at the same time. 

MarkownikofiT rule the MarkownikofF Rule specifies the orientation with which a small asymmetric molecule adds across the double bond of an alkene in an addition reaction. 

The acid-promoted cleavage of the cyclopropane ring similarly follows the Markownikoff rule. 

Other references related to the Markownikoff rule and <2/it/-Markownikoff rule are cited in literature. 

When additions take place by ionic mechanisms, they are catalyzed by either acids or bases. These additions follow the Markownikoff rule ... 

Acid-catalyzed additions to alkynes follow the Markownikoff rule. The initial addition products are not always stable, however. Addition of acetic acid, for example, results in the formation of enol acetates, which are easily converted to the corresponding carbonyl compound ... 

As will be indicated when the mechanism is discussed in more detail, discrete carbonium ions are not formed in all cases. An unsymmetrical alkene will nevertheless follow the Markownikoff rule, because the partial positive charge that develops will be located primarily at the carbon most able to accommodate the electron deficiency, that is, the most substituted one. 

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