Ch. 8 - Elimination ReactionsSee 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

Time to discuss the most complicated mechanism of the bunch, E2. It’s an awesome reaction, but there are a few extra details we’re gonna have to keep track of!

Concept #1: Drawing the E2 Mechanism.

Summary: A negatively charged nucleophile reacts with an inaccessible leaving group to produce beta-elimination in one-step.

Concept #2: Understanding the properties of E2.

Properties of E2 reactions:

  • Nucleophile =  Strong
  • Leaving Group =  Substituted
  • Reaction coordinate = Transition State
  • Reaction = Concerted
  • Rate =  Bimolecular
  • Rate =  k[Nu][RX]
  • Stereochemistry = Anti-Coplanar

Example #1: Rank the following alkyl halides in order of reactivity toward E2 reaction. 

Additional Problems
Which of the following is the correct mechanism for the elimination reaction of 2-bromo-2,3-dimethylbutane with methoxide?
Which of the following shows a mechanism for an E2 elimination?
Follow the curved arrows to predict the product(s) of the following chemical reactions
Which of the following shows the first step for an E2 reaction?
For the following E2 reaction, draw the transition state that leads to the predominant product(s), indicating geometry and stereochemistry with wedges and dashes. We will be paying particular attention to the geometry of your transition state. No need to show any arrows for moving electrons here, we are just interested in the transistion state and product structures. In your transition state structure, be sure to show bonds being made or broken as dotted lines
How many atoms and electrons are directly involved in the bond-making and bond-breaking of the first step in an E2 reaction? (A) five atoms, six electrons  (B) four atoms, six electrons (C) three atoms, six electrons  (D) five atoms, four electrons  (E) four atoms, four electrons  (F) three atoms, four electrons
How many alkenes would you expect to be formed from each of the following alkyl bromides under conditions of E2 elimination? Identify the alkenes in each case. (c) 3-Bromohexane  
How many alkenes would you expect to be formed from each of the following alkyl bromides under conditions of E2 elimination? Identify the alkenes in each case. (d) 2-Bromo-2-methylpentane 
How many alkenes would you expect to be formed from each of the following alkyl bromides under conditions of E2 elimination? Identify the alkenes in each case. (e) 2-Bromo-3-methylpentane. 
How many alkenes would you expect to be formed from each of the following alkyl bromides under conditions of E2 elimination? Identify the alkenes in each case.  (g) 3-Bromo-3-methylpentane 
In the dehydration of 2-bromo-2-methylbutane with potassium hydroxide, which hydrogen atom is preferentially abstracted? 
Which is the proper representation of the "flow" of electrons in this E2 elimination?
To question has multiple part, . Work all the parts to get the most points. Draw the major organic product in the sketch pad below. If the reaction produces a racemic mixture, draw both stereoisomers. 
What is the major product of the following reaction?a. Ib. IIc. Vd. IIIe. IV 
Provide the major organic product(s) in the reaction below.  
Draw the major organic product (other than ethanol) formed in the following reaction.
There are two benzylic bromides that give (E)-3, 5-dimethyl-2-phenyl-2-hexene in E2 elimination. Draw them. Use the wedge/hush bond tools to indicate stereochemistry. 
For the following dehydrohalogenation (E2) reaction, draw Zaitsev product(s), showing the stereochemistry clearly. If there is more than one organic product, both products can be drawn the same box. 
Draw the major organic product, of the reaction. Show the stereochemistry if applicable. Omiy byproducts such as water or bromide ion
Draw the products of the reaction shown. Electron flow is indicated with curved arrows.
For the following dehydrohalogenation (E2) reaction, draw the Zaitsev product(s) resulting from elimination involving C2-C3 (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 C2 or C3 and any carbon atom other than C3 or C2. 
For the following dehydrohalogenaton (E2) reaction, draw the major organic product(s), including stereochemistry. 
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 and any carbon atom other than C4.  
What product(s) are expected in the ethoxide-promoted beta-elimination reaction of 1-chloro-1-methylcyclohexane? Omit ions, salts, and ethanol from your response.  
Which of the following most readily undergoes an E2 reaction with sodium ethoxide (NaOCH2CH3)?a. (CH3)3CBr b. (CH3)3CCl c. (CH3)3Cl d. (CH3)3CF 
Which of the following is true of an E2 reaction? a. Base and substrate react together in a one step reaction b. A carbocation intermediate is formed in the reaction c. It is a two step reaction. d. The rate of the reaction is independent of base concentration