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Ch. 7 - Structure and Synthesis of Alkenes; Elimination
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh. 7 - Structure and Synthesis of Alkenes; EliminationProblem 55d,e
Chapter 7, Problem 55d,e

Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.
(d)
(e)

Verified step by step guidance
1
Step 1: Identify the reaction type. Dehydrohalogenation involves the elimination of a hydrogen atom and a halogen atom (Cl or Br) from adjacent carbon atoms, forming a double bond. This reaction typically occurs under the influence of a strong base, such as alcoholic KOH.
Step 2: Analyze the stereochemistry and structure of the alkyl halides. For compound (d), the chlorine atom is attached to a carbon adjacent to a hydrogen atom and a deuterium atom. For compound (e), there are two chlorine atoms on adjacent carbons, and one of the carbons is attached to a bulky tert-butyl group ((CH₃)₃C).
Step 3: Determine the possible elimination pathways. In compound (d), elimination can occur between the carbon bearing the chlorine atom and the adjacent carbon bearing the hydrogen atom (H) or the deuterium atom (D). The stereochemistry of the molecule will influence which hydrogen is eliminated. In compound (e), elimination can occur between either of the carbons bearing chlorine atoms and their adjacent hydrogens.
Step 4: Predict the major and minor products. For compound (d), elimination of the hydrogen atom (H) will likely be favored over deuterium (D) due to the kinetic isotope effect, resulting in the major product being the alkene formed by removing H. For compound (e), the bulky tert-butyl group will influence the regioselectivity of the elimination, favoring the formation of the more substituted alkene as the major product.
Step 5: Consider Zaitsev's rule. Zaitsev's rule states that the more substituted alkene is generally the major product in elimination reactions. Apply this rule to predict the major and minor products for both compounds (d) and (e).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Dehydrohalogenation

Dehydrohalogenation is an elimination reaction where a hydrogen halide (HX) is removed from an alkyl halide, resulting in the formation of an alkene. This reaction typically occurs under basic conditions, such as with alcoholic KOH, which promotes the elimination of HX. The regioselectivity of the reaction can lead to the formation of multiple products, including major and minor alkenes, depending on the stability of the resulting double bond.
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The dehydrohalogenation mechanism.

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene is generally the major product. This is because more substituted alkenes are more stable due to hyperconjugation and the inductive effect. When predicting products from dehydrohalogenation, it is essential to consider the possible alkene structures and identify which will be the most stable, guiding the prediction of major and minor products.
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Defining Zaitsev’s Rule

Stereochemistry of Alkenes

The stereochemistry of alkenes is crucial in determining the specific products formed during elimination reactions. Alkenes can exhibit cis/trans (or E/Z) isomerism based on the arrangement of substituents around the double bond. In the context of dehydrohalogenation, the stereochemical outcome can influence the stability and reactivity of the products, making it important to analyze the spatial arrangement of groups in the starting alkyl halide.
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Related Practice
Textbook Question

Write a balanced equation for each reaction, showing the major product you expect.

(d)

3
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Textbook Question

Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.

(f)

4
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Textbook Question

Using cyclohexane as your starting material, show how you would synthesize each of the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

a. bromocyclohexane

b. cyclohexene

c. ethoxycyclohexane

1
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Textbook Question

Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.

(a)

(b)

(c)

1
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Textbook Question

Using cyclohexane as your starting material, show how you would synthesize each of the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

d. 3-bromocyclohex-1-ene

e. cyclohexa-1,3-diene

f. cyclohexanol

1
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Textbook Question

Write a balanced equation for each reaction, showing the major product you expect.

(c)

4
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