Textbook Question
For each of the following alkyl halides, indicate the stereoisomer that would be obtained in greatest yield in an E2 reaction.
b. 4-bromo-2,2,3,3-tetramethylpentane
9. Alkenes and Alkynes
Zaitsev Rule
3:54 minutesProblem 22c
Textbook Question
What is the major elimination product obtained from the reaction of each of the following alkyl halides with hydroxide ion?
c. 
Verified step by step guidance1
Step 1: Identify the type of alkyl halide in the given structure. The molecule contains a bromine atom attached to a tertiary carbon, making it a tertiary alkyl halide. This is important because tertiary alkyl halides typically undergo elimination reactions via the E2 or E1 mechanism.
Step 2: Recall the elimination reaction mechanism. In the presence of a strong base like hydroxide ion (OH⁻), the reaction will likely proceed via the E2 mechanism. This involves the removal of a proton (β-hydrogen) from a carbon adjacent to the carbon bearing the leaving group (bromine), and simultaneous departure of the leaving group.
Step 3: Identify the β-hydrogens available for elimination. In the given structure, the β-hydrogens are located on the carbons adjacent to the carbon bonded to bromine. Analyze the structure to determine which β-hydrogens are accessible and which elimination pathway leads to the most stable alkene.
Step 4: Consider the stability of the possible alkene products. The major product of an elimination reaction is typically the more substituted alkene, as it is more stable due to hyperconjugation and alkyl group stabilization. In this case, elimination of a β-hydrogen from the carbon adjacent to the bromine will result in the formation of a double bond in the ring structure.
Step 5: Draw the major elimination product. The double bond will form between the carbon bearing the bromine and the adjacent carbon that loses a β-hydrogen. The resulting product will be a cyclobutene derivative with the double bond in the ring, as this is the most stable configuration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Elimination Reactions
Elimination reactions involve the removal of a leaving group and a hydrogen atom from adjacent carbon atoms, resulting in the formation of a double bond. In organic chemistry, these reactions are often classified as E1 or E2 mechanisms, depending on whether they occur in a stepwise or concerted manner. The nature of the alkyl halide and the base used can influence the pathway and the product distribution.
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Zaitsev's Rule
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is typically the major product. This is because more substituted alkenes are generally more stable due to hyperconjugation and the inductive effect. Understanding this rule helps predict the outcome of elimination reactions, especially when multiple alkene products are possible.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the context of elimination reactions, regioselectivity is influenced by factors such as sterics and stability of the resulting alkenes. Recognizing which alkene is favored can guide chemists in predicting the major product of a reaction involving alkyl halides.
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