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Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 115c
Chapter 10, Problem 115c

Draw the products of each of the following SN2/E2 reactions. If the products can exist as stereoisomers, show which stereoisomers are formed.
c. (3S,4R)-3-bromo-4-methylhexane + CH3O−

Verified step by step guidance
1
Analyze the reaction type: The problem specifies SN2/E2 reactions. SN2 (bimolecular nucleophilic substitution) and E2 (bimolecular elimination) are competing mechanisms. The choice depends on the substrate, nucleophile/base, and reaction conditions. Here, CH3O− is a strong nucleophile and a strong base, so both SN2 and E2 are possible.
Examine the substrate: The substrate is (3S,4R)-3-bromo-4-methylhexane. The bromine atom is attached to the 3rd carbon, making it a good leaving group. The stereochemistry at the 3rd carbon is S, and the 4th carbon has an R configuration with a methyl group attached.
Consider the SN2 pathway: In an SN2 reaction, the nucleophile (CH3O−) attacks the carbon bonded to the leaving group (C-3) from the opposite side, leading to an inversion of configuration at C-3. This results in a product with the 3rd carbon having an R configuration. The stereochemistry at C-4 remains unchanged (R).
Consider the E2 pathway: In an E2 reaction, the base (CH3O−) abstracts a β-hydrogen (a hydrogen on a carbon adjacent to the carbon bearing the leaving group). Here, β-hydrogens are available on both C-2 and C-4. Elimination of H from C-2 forms a double bond between C-2 and C-3, while elimination of H from C-4 forms a double bond between C-3 and C-4. The resulting alkenes can have E/Z stereoisomers depending on the spatial arrangement of substituents around the double bond.
Draw the products: For the SN2 pathway, draw the product with inversion of configuration at C-3. For the E2 pathway, draw the two possible alkenes (one with a double bond between C-2 and C-3, and the other with a double bond between C-3 and C-4), showing both E and Z stereoisomers for each alkene. Ensure the stereochemistry at C-4 remains consistent with the original R configuration.

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Key Concepts

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

S<sub>N</sub>2 Mechanism

The S<sub>N</sub>2 mechanism is a type of nucleophilic substitution reaction where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction occurs in a single concerted step, leading to inversion of configuration at the carbon center. It is favored by primary and some secondary substrates, particularly in polar aprotic solvents.
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E2 Mechanism

The E2 mechanism is a bimolecular elimination reaction where a base abstracts a proton from a β-carbon while a leaving group departs from the α-carbon, resulting in the formation of a double bond. This reaction requires a strong base and typically occurs in a single concerted step. The stereochemistry of the reaction is important, as it often leads to the formation of specific geometric isomers.
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Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In the context of S<sub>N</sub>2 and E2 reactions, stereoisomers can arise due to the configuration of chiral centers or the geometry of double bonds. Understanding stereoisomerism is crucial for predicting the products of these reactions, as different stereoisomers can exhibit distinct physical and chemical properties.
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Related Practice
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Draw the structures of the products obtained from the following reaction:

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Explain why the rate of the reaction of 1-bromo-2-butene with ethanol is increased if silver nitrate is added to the reaction mixture.

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How could you prepare the following compounds from the given starting materials?

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Textbook Question

Draw the products of each of the following SN2/E2 reactions. If the products can exist as stereoisomers, show which stereoisomers are formed.

a. (3S,4S)-3-bromo-4-methylhexane + CH3O−

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Textbook Question

Two elimination products are obtained from the following E2 reaction:

a. What are the elimination products?

b. Which is formed in greater yield?

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Textbook Question

Draw the products of each of the following SN2/E2 reactions. If the products can exist as stereoisomers, show which stereoisomers are formed.

b. (3R,4R)-3-bromo-4-methylhexane + CH3O−

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