Saytzev’s rule

The data in Table 2.2 are representative of many elimination reactions. The product distribution is found to depend on whether the substrate is neutral (with a halide or sulfonate leaving group) or positively charged (with a —N(CH3)3 or —S(CH3)2 leaving group — which become N(CH3)3 and S(CH3)2 respectively). The empirical rules linking the nature of the substrate and the product distribution are known as Saytzev s rule and Hofmann s rule. 

If elimination were to proceed by the E2 mechanism. Compound 3.1 would be expected to obey Saytzev s rule and give the more substituted alkene (Structure 3.3), whereas Compound 3.2 should give predominantly the less substituted product (Structure 3.4) according to Hofmann s rule. 

This is indeed the experimental result, and the predominant alkene formed from 3.1 and 3.2 by an El mechanism is 3.3, the more substituted alkene (that is, the more thermodynamically stable for both substrates). El reactions are generally found to obey Saytzev s rule, whatever the leaving group... 

With some substrates, elimination can occur in two directions, to give different alkene products. Saytzev s rule states that neutral substrates give predominantly the more substituted alkene, by the E2 mechanism. Hofmann s rule applies to charged substrates, such as sulfonium and ammonium salts, and these give a predominance of the less substituted alkene by the bimolecular mechanism. 

El reactions usually obey Saytzev s rule to give the more substituted alkene. Since the more stable alkene is formed, the E form predominates. 

The Saytzev s Rule and Hofmann s Rule can be used to predict the orientation of elimination, and the stereochemistry is preferentially antiperiplanar. 

In cyclic systems, the usual simple requirements of Saytzev or Hofmann rules may be overridden by other special requirements of the system, e.g. the preference for elimination from the truns-diaxial conformation in cyclohexane derivatives (cf. p. 255). Another such limitation is that it is not normally possible to effect an elimination so as to introduce a double bond on a bridgehead carbon atom in a fused ring system (Bredt s rule), e.g. (47) (48) ... 

SaytzefPs rule The German spelling of Zaitsev s rule. Also sometimes spelt Saytzev. 

Whenever an elimination occurs to give the more stable, more highly substituted alkene, chemists say that the elimination follows Zaitsev s rule, named for the nineteenth-century Russian chemist A. N. Zaitsev (1841—1910) who formulated it. (Zaitsevs name is also transliterated as Zaitzev, Saytzeff, Saytseff, or Saytzev.)... 

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