Textbook Question
Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely.
b. 2−chlorohexane + NaOCH3 in methanol
1
views
Ch. 7 - Structure and Synthesis of Alkenes; Elimination
Wade9th EditionOrganic ChemistryISBN: 9780135213728
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 7, Problem 32a
Predict the major and minor elimination products of the following proposed reactions (ignoring any possible substitutions for now). In each case, explain whether you expect the mechanism of the elimination to be E1 or E2.
(a) 
Verified step by step guidance1
Step 1: Analyze the reaction conditions. The presence of NaOCH2CH3 (a strong base) and CH3CH2OH (a polar protic solvent) under heat suggests that the elimination mechanism is likely E2. E2 mechanisms are favored by strong bases and heat, and they occur in a single concerted step.
Step 2: Identify the substrate. The substrate is a secondary alkyl bromide. Secondary alkyl halides can undergo both E1 and E2 mechanisms, but the strong base and heat strongly favor E2.
Step 3: Determine the major and minor elimination products. In an E2 reaction, the base abstracts a proton from a β-carbon (a carbon adjacent to the carbon bonded to the leaving group). The major product is determined by Zaitsev's rule, which states that the more substituted alkene is favored. The minor product will be the less substituted alkene.
Step 4: Apply anti-periplanar geometry. In E2 reactions, the β-hydrogen and the leaving group (Br) must be anti-periplanar (opposite sides of the same plane). This stereoelectronic requirement influences which β-hydrogen is abstracted and thus the product distribution.
Step 5: Draw the major and minor products. The major product will be the more substituted alkene formed by elimination of a β-hydrogen from the carbon with more substituents. The minor product will be the less substituted alkene formed by elimination of a β-hydrogen from the less substituted β-carbon.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
4mWas this helpful?
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. The two main types of elimination mechanisms are E1 and E2. E1 is a two-step process where the leaving group departs first, forming a carbocation, followed by deprotonation. E2 is a one-step concerted mechanism where the base abstracts a proton while the leaving group exits simultaneously.
Recommended video:
Guided course
00:40
Recognizing Elimination Reactions.
E1 vs. E2 Mechanisms
The E1 mechanism is favored in polar protic solvents and with substrates that can stabilize carbocations, such as tertiary or allylic halides. In contrast, the E2 mechanism requires a strong base and is favored in polar aprotic solvents, typically involving primary or secondary substrates. The choice between E1 and E2 can significantly affect the product distribution and reaction rate.
Recommended video:
Guided course
09:36Drawing the E2 Mechanism.
Regioselectivity in Elimination
Regioselectivity refers to the preference for the formation of one constitutional isomer over another in a chemical reaction. In elimination reactions, this can lead to major and minor products based on the stability of the resulting alkenes. The more substituted alkene is generally favored due to greater stability, following Zaitsev's rule, while less substituted products may form under certain conditions, such as steric hindrance or the use of bulky bases.
Recommended video:
Guided course
00:38Intro to Substitution/Elimination Problems
Related Practice
Textbook Question
Predict which of the following compounds will undergo elimination with KOH faster, and explain why. Predict the major product that will be formed.
Textbook Question
Give the expected product(s) of E2 elimination for each reaction. (Hint: Use models!)
(a)
7
views
Textbook Question
Predict the major and minor elimination products of the following proposed reactions (ignoring any possible substitutions for now). In each case, explain whether you expect the mechanism of the elimination to be E1 or E2.
(b)
1
views
Textbook Question
Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely.
a. 1−bromohexane + sodium ethoxide in ethanol
1
views
Textbook Question
Give the expected product(s) of E2 elimination for each reaction. (Hint: Use models!)
(b)
1
views