Definition of Saytzeff Rule. What is the Saytzeff Rule? Dehydrohalogenation of secondary- and tertiary-alkyl halides proceeds by the preferential removal of the . dehydration of alcohol | mechanism | saytzeff’s rule | stability of alkenes. 22 Jul The Zaitsev’s Rule (or Saytzeff rule) draws our attention to the alternate possibility . On elimination of HX, the more stable olefin is obtained (Fig.
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E2 eliminations require anti -periplanar geometry, in which the proton and leaving group lie on opposite sides of the C-C bond, but in the same plane. The quaternary ammonium group is large, and interactions with alkyl groups on the rest of the molecule are undesirable.
Zaitsev was not the first chemist to publish the rule that now bears his name. As a result, the Hofmann Product is typically favored when using bulky bases. The Cope elimination is very similar to the Hofmann elimination in principle, but occurs under milder conditions.
The rule makes no generalizations about the stereochemistry of the newly formed alkene, but only the regiochemistry of the elimination reaction. In some cases, the stereochemistry of the starting material can prevent the formation of the Sqytzeff product.
So by looking at the number of alkyl groups attached to the alkene, the degree of substitution and hence major and minor products can be determined. Examining the heats of hydrogenation for various alkenes reveals that stability increases with the amount of substitution.
Aleksandr Nikolaevich Popov gule an empirical rule similar to Zaitsev’s in and presented his findings at the University of Kazan in The amount of energy released during a hydrogenation reaction, known as the heat of hydrogenation, is inversely related to the stability of the starting alkene: Due to steric interactions, a bulky base — such as potassium t-butoxidesaytseffor 2,6-lutidine — cannot readily abstract the proton that would lead to the Zaitsev product.
For butene, it has 2 alkyl groups attached to the alkene. More generally, Zaitsev’s rule predicts that in an elimination reaction, the most substituted product will be the most stable, and therefore the most favored.
For example, when menthyl chloride is treated with sodium ethoxide, the Hofmann product is formed exclusively: For a step-by-step guide to predict the major product using Saytzeff Rule, check out this video lesson now! In an alkane, the maximum separation is that of the tetrahedral bond angle, These intramolecular interactions are relevant to the distribution of products in the Hofmann elimination reaction, which converts amines to alkenes.
How to predict Major Product for Elimination Reaction. Bulletin for the History of Chemistry. Zaitsev and Markovnikov both studied under Alexander Butlerovtaught at the Ruel of Kazan during the same period, and were bitter rivals.
Justus Liebigs Annalen der Chemie. Operational Organic Chemistry 4th ed. While Zaitsev’s paper was well referenced throughout the 20th century, it was not until the s that textbooks began using the term “Zaitsev’s rule. As a result, the separation between alkyl groups is greatest in the most substituted alkene.
Consequently, a terminal methyl group rhle has no alkyl substituent is more acidic than the internal methine proton bearing at least one sajtzeff substituent. Markovnikov, who published in what is now known as Markovnikov’s ruleand Zaitsev held conflicting views regarding elimination reactions: While at the University of KazanRussian chemist Alexander Zaitsev studied a variety of different elimination reactions and observed a general trend in the resulting alkenes.
As a result, this particular reaction produces only the Hofmann product. Also, alkyl groups are sterically saytzsff, and are most stable when they are far away from each other. The apparent contradiction in this set of rules is easily resolved through a critical look at the mechanisms involved in these two sets of reaction conditions.
Justus Liebig’s Annalen der Chemie.
To make it easier to visualise, we can box up the alkene and count the number of alkyl groups attached to the alkene. On elimination of HX, the more stable olefin is obtained Fig 2.