Alkanes halogenations

In contrast to the free radical substitution observed when halogens react with alkanes halogens normally react with alkenes by electrophilic addition... 

The chemical resistance of polyethylene is, to a large measure, that expected of an alkane. It is not chemically attacked by non-oxidising acids, alkalis and many aqueous solutions. Nitric acid oxidises the polymer, leading to a rise in power factor and to a deterioration in mechanical properties. As with the simple alkanes, halogens combine with the hydrocarbon by means of substitution mechanisms. 

Although interesting from a mechanistic point of view, alkane halogenation is a poor synthetic method for preparing alkyl halides because mixtures of products invariably result. For example, chlorination of methane does not stop cleanly at the monochlorinated stage but continues to give a mixture of dichloro, trichloro, and even tetrachloro products. 

This allylic bromination with NBS is analogous to the alkane halogenation reaction discussed in the previous section and occurs by a radical chain reaction pathway. As in alkane halogenation, Br- radical abstracts an allylic hydrogen atom of the alkene, thereby forming an allylic radical plus HBr. This allylic radical then reacts with Br2 to yield the product and a Br- radical, which cycles back... 

Alkane Halogen Alkyl halide Hydrogen halide... 

Maleic acid, 338 Maionic ester, 380 Markovnikoff s rule, 96 Mass spectroscopy, 247/T Mechanism, alcohol dehydration, 92 alkane halogenation, 56 benzyne, 217 El and E2, UOff SnI and Sn2, 122 ... 

In more complex alkanes, halogenation can occur to some extent at all positions to give a mixture of monosubstituted products. For example, bromination of propane produces a mixture of 1-bromopropane and 2-bromopropane. 

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