Saytzeff rule

In dehydration and dehydrohalogenation the preferential order for removal of an H is 3°>2°> 1 (Saytzeff rule). We can say the poor get poorer. This order obtains because the more R s on the C==C group, the more stable is the alkene. The stability of alkenes in decreasing order of substitution by R is... 

Over most catalysts, with the notable exception of thoria [130], the thermodynamically more stable olefins are formed (Saytzeff rule) as primary products when two elimination directions are possible. This is in agreement with the results concerning other elimination reactions, both in the liquid phase (cf. refs. 64 and 65) and over solid catalysts. The striking difference in the action of thoria has been explained on the basis of a different mechanism [68],... 

The reaction has been extensively used for the determination of the structure of naturally occurring bases (e.g. the alkaloids). However it has rather limited preparative value, even though the elimination reaction occurs without any rearrangement of the carbon skeleton, and the regioisomer which predominates in the product is the less highly substituted alkene (Hofmann rule contrast the Saytzeff rule). Such alkenes are now more usually prepared by other procedures noted below. 

Saytzeff rule states that the major product of elimination will be the most substituted alkene. 

Saytzeff Rule implies that base-induced eliminations (E2) will lead predominantly to the olefin in which the double bond is more highly substituted, i.e. that the product distribution will be controlled by thermodynamics. 

The use of sterically hindered bases raises the activation energy barrier for the pathway to the product predicted by Saytzeffs Rule. Thus, a sterically hindered base will preferentially react with the least hindered protons, and the product distribution will be controlled by kinetics. 

And the most stable alkene (most substituted) is the usual product (Saytzeff rule). 

The Saytzeff rule (or Zaitsev s rule or Saytsev s rule named after Alexander Mikhailovich Zaitsev) implies that base (sterically unhindered) induced eliminations will lead predominantly to the alkene in which the double bond is more highly substituted. However, if the base, for example, is potassium f-butoxide [(CH3)3COK], the bulkiness prohibits the base from pulling the proton off of the most substituted carbon. In such cases, the less substituted alkene, i.e. Hofmann elimination, is preferred. 

This phenomenon is called the Zaitsev rule (also called the Saytzeff rule, depending on the translation) for the Russian chemist who first noted this trend. 

Each step of this E, elimination reaction is reversible and thus the reaction is driven to completion by removing one of the products, the alkene. In these reactions several alkenes can be produced. The Saytzeff rule states that the more substituted alkene is the more stable and thus the one formed in larger amount. And the trans isomer is more stable than the cis isomer. With this information it should be possible to deduce which peaks on the gas chromatogram correspond to a given alkene and to predict the ratios of the products. 

Problem 14.11 Like Markovnikov, Saytzeff stated his rule in terms, not of product stability, but of numbers of hydrogens on carbon atoms, (a) Suggest a wording for this original Saytzeff rule, (b) Predict the major product of dehydrohalogena-tion of 2-bromo-l-phenylbutane on the basis of the original rule, (c) On the basis of the modern rule. 

Saytzeff Rule. When a halide is converted to an olefin, the most highly branched olefin will be formed. 

In a careful study of elimination reactions designed to determine whether the differences between the Hofmann and the Saytzeff rules might be due to the nature of the alkyl compound (halide or onium), the... 

It is clear that in order to employ the Hofmann rule we must be sure that the reaction is following second-order kinetics. The Saytzeff rule, however, appears to be perfectly general. 

Dehydrohalogenation. H. C. Brown found that in cases where elimination of HX with potassium ethoxide follows the Saytzeff rule and gives mainly the internal... 

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