Hydrogen halide addition

REGIOSELECTIVITY OF HYDROGEN HALIDE ADDITION MARKOVNIKOV S RULE... 

Regioselectivity of Hydrogen Halide Addition Markovnikovs Rule... 

Carbocation Rearrangements in Hydrogen Halide Addition to Alkenes... 

CARBOCATION REARRANGEMENTS IN HYDROGEN HALIDE ADDITION TO ALKENES... 

Sections See Table 6 6 Hydrogen halide addition to alkenes proceeds by elec... 

The order of reactivity of the hydrogen halides is HI > HBr > HCl, and reactions of simple alkenes with HCl are quite slow. The studies that have been applied to determining mechanistic details of hydrogen halide addition to alkenes have focused on the kinetics and stereochemistry of the reaction and on the effect of added nucleophiles. The kinetic studies often reveal complex rate expressions which demonstrate that more than one process contributes to the overall reaction rate. For addition of hydrogen bromide or Itydrogen... 

It is not difficult to incorporate this result into the general mechanism for hydrogen halide additions. These products are formed as the result of solvent competing with halide ion as the nucleophilic component in the addition. Solvent addition can occur via a concerted mechanism or by capture of a carbocation intermediate. Addition of a halide salt increases the likelihood of capture of a carbocation intermediate by halide ion. The effect of added halide salt can be detected kinetically. For example, the presence of tetramethylammonium... 

As in the case of hydrogen halide additions, this mode of attack should lead to anti addition. 

We can gain a general understanding of the mechanism of hydrogen halide addition to alkenes by extending some of the principles of reaction mechanisms introduced earlier. In Section 5.12 we pointed out that carbocations are the conjugate acids of alkenes. Therefore, strong acids such as HCI, HBr, and HI can protonate the double bond of an alkene to fonn a car bocation. 

Cleavage of epoxides with hydrogen halides Addition of hypohalous acids to alkenes... 

In contrast to the work of Peterson (38) with 3-hexyne in trifluoroacetic acid (vide supra), no trimeric adducts were observed in the hydrogen halide additions to propyne (48). 

The diminished stereospecificity is similar to that noted for hydrogen halide addition to phenyl-substituted alkenes. 

Ample results may be drawn from the sugar series on the subject of hydrogen halide addition to epoxidee, some of wbiob has only been recently found to be m error and corrected. 

See Table 6.6. Hydrogen halide addition to alkenes proceeds by electrophilic attack of the reagent on the tt electrons of the double bond. Car-bocations are intermediates. 

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