Russian chemist, Alexander Zaitsev (also pronounced as Saytzeff) who in formulated a rule which can be summarised as “ in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms .” Thus, -bromopentane gives pent- -ene as the major product. . Reaction with metals Most organic chlorides, bromides and iodides react with certain metals to give compounds containing carbon-metal bonds. Such compounds are known as organo-metallic compounds .
An important class of organo-metallic compounds discovered by Victor Grignard in is alkyl magnesium halide, RMgX, referred as Grignard Reagents . These reagents are obtained by the reaction of haloalkanes with magnesium metal in dry ether. A chemical reaction is the result of competition; it is a race that is won by the fastest runner. A collection of molecules tend to do, by and large, what is easiest for them.
An alkyl halide with b -hydrogen atoms when reacted with a base or a nucleophile has two competing routes: substitution (S N and S N ) and elimination. Which route will be taken up depends upon the nature of alkyl halide, strength and size of base/nucleophile and reaction conditions. Thus, a bulkier nucleophile will prefer to act as a base and abstracts a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa . Similarly, a primary alkyl halide will prefer a S N reaction, a secondary halide- S N or elimination depending upon the strength of base/nucleophile and a tertiary halide- S N or elimination depending upon the stability of carbocation or the more substituted alkene.