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What is Zaitsev's Rule?

Nicholas Amendolare, Amanda Robb
  • Author
    Nicholas Amendolare

    Nicholas Amendolare is a high school and middle school science teacher from Plymouth, Massachusetts. He has a bachelor's degree in environmental science from Worcester Polytechnic Institute and a master's degree in education from Harvard University. He has been a teacher for nine years, has written for TED-Ed, and is the founder of www.MrAscience.com.

  • Instructor
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Explore Zaitsev's rule. Learn the definition of Zaitsev's rule and understand its characteristics. See the difference between Zaitsev and Hoffman products. Updated: 04/11/2022

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What is Zaitsev's Rule?

Within the field of organic chemistry, Zaitsev's rule is a rule of thumb for predicting the alkene products produced by elimination reactions. Russian chemist Alexander Zaitsev studied a wide variety of elimination reactions in the 1870s. He observed a general trend: the alkene formed in the greatest amount was usually that which corresponded to the removal of the hydrogen from the alpha-carbon having the fewest hydrogen substituents. In other words, Zaitsev's rule predicts that the most common product will be the most stable, meaning the one that contains the most carbon-carbon bonds.


A portrait of Russian chemist Alexander Zaitsev.

A portrait of Alexander Zaitsev.


While it is a useful rule for predicting the favored product in many elimination reactions, Zaitsev's rule has many exceptions. Many of them include exceptions when "Hoffman products" are produced. The Hoffman product is the less substituted alkene produced by an elimination reaction. These include compounds having quarternary nitrogen, {eq}NR_{3}+ {/eq}, and {eq}SO_{3}H {/eq}. In these eliminations, the Hofmann product is preferred. However, if the leaving group contains halogens other than fluorine, then the Zaitsev product is typically produced. For example, an elimination reaction using hydroxide ions as the base will most likely follow the Zaitsev rule and result in the formation of a tetra-substituted alkene. Another exception to this rule involves steric hindrance, if a molecule has much steric hindrance, elimination will favor the production of Hoffman products. Steric hindrance involves the molecule becoming less reactive due to the large size and space taken up by high-mass substituents.

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Characteristics of Zaitsev's Rule

In organic chemistry, an elimination reaction is any organic chemical reaction in which groups of atoms are removed from a molecule. Usually, this occurs through the action of acids, bases, and metals. When predicting the products produced by elimination reactions, there are often multiple possibilities. This is what inspired Alexander Zaitsev to publish his paper describing the rule, although interestingly, it was not until the 1960s that chemistry textbooks began calling it "Zaitsev's rule." Zaitsev's rule has three important characteristics, as outlined below.

  1. If multiple products are possible, the more common alkene tends to be the major product. The alkene which is "tetrasubstituted," meaning attached to four carbon atoms, or the molecule that is the most substituted carbon, is often the major product, rather than the "disubstituted" alkene, which would be attached to two carbon atoms and two hydrogen atoms. According to Zaitsev's rule, the products that produce more carbon-carbon bonds will also be more stable and will be produced more often.
  2. Alkenes become more stable as carbon-hydrogen bonds are replaced with carbon-carbon bonds. As an alkene becomes more substituted, containing more carbon and less hydrogen, it becomes more thermodynamically stable in a process known as hyperconjugation. This allows for the trend we see in elimination reactions: the major product tends to be the more-substituted alkene because the transition state is lower in energy and easier to achieve.
  3. Elimination will occur so that hydrogen is removed from the beta-carbon with the fewest hydrogen atoms. This is essentially the modern form of Zaitsev's rule. In organic chemistry, the alpha-carbon is the carbon atom attached to the leaving group, while the beta-carbons are any carbon atoms attached to the alpha-carbon.


An example of a chemical reaction following the Zaitsev rule.

An example of a chemical reaction following the Zaitsev rule.


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Frequently Asked Questions

Why is the Zaitsev product more stable?

In organic chemistry, elimination reactions often follow Zaitsev's rule. The rule states that, when more than one alkene product is formed, the one with more double bonds will be more stable and therefore more common.

What does Zaitsev's rule say?

In organic chemistry, Zaitsev's rule says that in an elimination reaction involving alkenes the most common product will be the most stable product. However, Zaitsev's rule has many exceptions, specifically when reactions involve quarternary nitrogens.

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