Organic Chemistry

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9. Alkenes and Alkynes

Zaitsev Rule

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Elimination reactions often can yield multiple products. However, not all of these products will be of equal stability. Zaitsev’s Rule (also spelled Saytzeff’s Rule) helps us predict the major product. 

Zaitsev vs. Hofmann Product

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concept

Defining Zaitsev’s Rule

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Zaitsev’s Rule predicts that in most cases, the most substituted product will be favored. This is also known as the Zaitsev product. Draw the Zaitsev product of the following reaction:

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Zaitsev product

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The exception to this rule comes with the use of bulky bases. These promote the formation of the les substituted product.

  • The most common bulky bases are lithium diisopropylamide (LDA) and tert-butoxide (t-BuO-)

The less substitued product is called the Hofmann product. Let's draw the Hofmann product of the following reaction: 

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Hofmann product

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Thermodynamic vs. Kinetic Product

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Using a Free Energy Diagram to explain thermodynamic vs. kinetic products.

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  • The Zaitsev product is also known as the thermodynamic product, since it is the one that releases the most free energy overall (most negative ΔG°).
  • The Hofmann product is also known as the kinetic product, since it is the one that overcomes the lowest activation energy (Ea). 

Practice

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Problem

What is the major product of the reaction?

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Problem

What is the major product of the reaction?

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Problem

What is the major product of the reaction?