Ch. 9 - Alkenes and AlkynesSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

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

Concept #1: Defining Zaitsev’s Rule

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:

Example #1: An example of a Zaitsev product.

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: 

Example #2: An example of a Hofmann product.

Thermodynamic vs. Kinetic Product

Concept #2: Using a Free Energy Diagram to explain thermodynamic vs. kinetic products. 

  • 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

Practice: What is the major product of the reaction?

Practice: What is the major product of the reaction?

Practice: What is the major product of the reaction?

Additional Problems
Which compound would most readily form the depicted alkene through an E2 mechanism?
Write structural formulas for all the alkene products that could reasonably be formed from each of the following compounds under the indicated reaction conditions. Where more than one alkene is produced, specify the one that is the major product. (b) 1-Methylcyclopentyl chloride (sodium ethoxide, ethanol, 70°C)    
When 2-bromo-2-methylbutane is treated with a base, a mixture of 2-methyl-2-butene and 2-methyl-1-butene is produced. When potassium hydroxide is the base, 2-methyl-1-butene accounts for 45% of the mixture. But when potassium tert-butoxide is the base, 2-methyl-1-butene accounts for 70% of the mixture. What would you predict for the percent of 2-methyl-1-butene in the mixture if potassium propoxide were the base? a) less than 45% b) 45% c) between 45% and 70% d) more than 70%
Provide the major product for the following compound.
Provide structures for the major and minor products of the following reaction and indicate which type of reaction it follows: SN1, SN2, E1, or E2. In addition, also provide the IUPAC names of both the major and minor product. As a bonus, indicate if the products (major/minor) and reaction would be different if LDA was used instead.   
Predict the major elimination product for the following reaction:
For the reaction shown below, draw the structure of the major product(s). Where appropriate, write "No Reaction". Assume all chiral starting materials are optically pure. Show stereochemistry where appropriate. Indicate whether the product exists as a single enantiomer or a racemic mixture.
Using Zaitsevʹs rule, choose the most stable alkene among the following.A) cis-3,4-dimethylcyclohexeneB) 1,6-dimethylcyclohexeneC) 1,2-dimethylcyclohexeneD) They are all of equal stability according to Zaitsevʹs rule.
Supply Reagents:
Predict the product WITH Stereochemistry:
The stereoselectivity of elimination of 5-bromononane on treatment with potassium ethoxide was described in Section 5.14. Draw Newman projections of 5-bromononane showing the conformations that lead to cis -4-nonene and trans -4-nonene, respectively. Identify the proton that is lost in each case, and suggest a mechanistic explanation for the observed stereoselectivity.
Predict the product(s).
Be sure to answer all parts.Draw both the SN1 and E1 products of the following reaction. 
Draw an alkyl bromide that, upon treatment with base, will give the compound shown. Indicate the proper relative stereochemistry.
Which of the following would be the best base for performing the following elimination? Select all that apply.
Draw the major organic product of the following reaction. Indicate the stereochemistry, if appropriate. wavy bond to indicate a mixture of configurations.
What is the major organic product of the following reaction?a. 2, 3-dimethyl-1-hexene b. 2, 3-dimethyl-2-hexene c. 2-isopropyl-1-pentene d. (Z)-2, 3-dimethyl-3-hexene e. (E)-2, 3-dimethyl-3-hexene
Draw the major elimination product formed in the following reaction.  
Draw the structure of the major product formed in the following reaction. 
Draw the major organic product formed when the structure shown below undergoes a reaction with t-BuONa.
Provide the major organic product of the following reaction.  
What is the major product of the elimination reaction?a. Ib. IVc. IIId. II  
For the following dehydrohalogenation (E2) reaction, draw the Zaitsev product(s) resulting from elimination involving C3-C4 (i.e., the carbon atoms depicted with stereobonds). Show the product stereochemistry clearly. If there is more than one organic product, both products may be drawn in the same box. Ignore elimination involving C3 or C4 and any carbon atom other than C4 or C3.
For the following dehydrohalogenation (E2) reaction, draw the major organic product(s), including stereochemistry.
For the following dehydrohalogenation (E2) reaction, draw the major organic product(s), including stereochemistry.
For the following dehydrohalogenation (E2) reaction, draw the major organic product(s), including stereochemistry.
Question 11What is the major product of the following reaction?
What is (are) the product(s) of the following reaction? • I and II • II and III • I and III • I, II and III  
What is the major elimination product obtained from the following reaction?