Alkene From halide

Preparing Alkyl Halides from Alkenes Allylic Bromination 339... 

Another method for preparing alkyl halides from alkenes is by reaction with jV-brotnosuccinimide (abbreviated NBS) in the presence of light to give products resulting from substitution of hydrogen by bromine at the allylic position—the position next to the double bond. Cyclohexene, for example, gives 3-bromo-cyclohexene. 

Problem 6.27 Why are dry gaseous hydrogen halides (HX) acids and not their aqueous solutions used to prepare alkyl halides from alkenes ... 

Benzylic halides can be prepared by the same radical-halogenating agents that give allylic halides from alkenes. These include Cl2, Br2, N-bromo-succinimide (Section 14-3A), S02C12, and im-butyl hypochlorite (see Exercise 4-18) ... 

Isohypsic reactions of alkenes, like electrophilic additions of H2O or HX, represent a conventional pathway for the preparation of alcohols and alkyl halides from alkenes. The scope of their application was originally limited as unsymmetrical alkenes (e.g. 125) gave product mixtures composed of both Markovnikov (M) adducts and anti-Markovnikov (aM) adducts. As was already mentioned above (see Scheme 2.10), an efficient and general method for the conversion of alkenes into alcohols or ethers 126 (Scheme 2.47), with a nearly complete M selectivity, was elaborated using mercury salts as electrophiles in conjunction with the reduction of the formed adducts. It is also... 

PREPARING ALKYL HALIDES FROM ALKENES ALLYLIC BROMINATION... 

We ve already seen several methods for preparing alkyl halides from alkenes, including the reactions of HX and X2 with alkenes in electrophilic addition reactions (Sections 7.7 and 8.2). The hydrogen halides HCl, HBr, and HI react with alkenes by a polar mechanism to give the product of Markovnikov... 

Organomercury compounds have had limited use in synthesis. One promising procedure, based on the availability of the mercury compounds from alkenes via organoboranes, is the synthesis of primary halides from alkenes. This procedure has the opposite regioselectivity to the direct ionic addition of hydrogen bromide... 

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