Skip to main content
Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.6 - Alkyl Halides; Nucleophilic SubstitutionProblem 27d,e
Chapter 6, Problem 27d,e

For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).
d. cyclohexylbromide + methanol
e. cyclohexylbromide + sodium ethoxide

Verified step by step guidance
1
Step 1: Analyze the substrate (cyclohexylbromide) in both reactions. Cyclohexylbromide is a secondary alkyl halide, which means it can undergo both SN1 and SN2 mechanisms depending on the reaction conditions.
Step 2: For reaction (d) with methanol, consider the nucleophile and solvent. Methanol is a weak nucleophile and a polar protic solvent. Weak nucleophiles and polar protic solvents favor the SN1 mechanism. The reaction will likely proceed via a carbocation intermediate, and the substitution product will involve methanol replacing the bromide group.
Step 3: For reaction (e) with sodium ethoxide, consider the nucleophile and solvent. Sodium ethoxide is a strong nucleophile and a strong base. Strong nucleophiles favor the SN2 mechanism, especially with secondary alkyl halides. The reaction will likely proceed via a concerted mechanism where the ethoxide ion directly displaces the bromide group.
Step 4: Predict the substitution product for each reaction. In reaction (d), the product will be cyclohexylmethoxy (cyclohexane with a methoxy group replacing the bromide). In reaction (e), the product will be cyclohexylethoxy (cyclohexane with an ethoxy group replacing the bromide).
Step 5: Summarize the mechanisms. Reaction (d) proceeds predominantly via the SN1 mechanism due to the weak nucleophile and polar protic solvent. Reaction (e) proceeds predominantly via the SN2 mechanism due to the strong nucleophile and strong base.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
10m
Was this helpful?

Key Concepts

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

Nucleophilicity

Nucleophilicity refers to the strength of a nucleophile, which is a species that donates an electron pair to form a chemical bond. Strong nucleophiles, such as alkoxides, are more likely to participate in bimolecular nucleophilic substitution (SN2) reactions, while weak nucleophiles, like alcohols, tend to favor unimolecular nucleophilic substitution (SN1) mechanisms. Understanding the nucleophile's strength is crucial for predicting the reaction pathway.
Recommended video:
Guided course
08:27
Nucleophilic Addition

SN1 vs. SN2 Mechanisms

SN1 and SN2 are two distinct mechanisms of nucleophilic substitution reactions. SN1 is a first-order reaction that involves the formation of a carbocation intermediate, typically favored by tertiary substrates and weak nucleophiles. In contrast, SN2 is a second-order reaction that occurs in a single concerted step, requiring strong nucleophiles and is generally unfavorable for tertiary substrates due to steric hindrance.
Recommended video:
Guided course
10:49
Drawing the SN1 Mechanism

Substrate Structure

The structure of the substrate, particularly the degree of substitution at the carbon atom bonded to the leaving group, significantly influences the reaction mechanism. Primary (1°) substrates favor SN2 reactions, while tertiary (3°) substrates favor SN1 due to carbocation stability. Secondary (2°) substrates can undergo either mechanism depending on the nucleophile's strength and the reaction conditions, making substrate structure a key factor in predicting reaction outcomes.
Recommended video:
Guided course
03:04
Drawing Resonance Structures
Related Practice
Textbook Question

For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).

a. 2-chloro-2-methylbutane + CH3COOH

b. isobutylbromide + sodium methoxide

819
views
Textbook Question

A reluctant first-order substrate can be forced to ionize by adding some silver nitrate (one of the few soluble silver salts) to the reaction. Silver ion reacts with the halogen to form a silver halide (a highly exothermic reaction), generating the cation of the alkyl group.

Give mechanisms for the following silver-promoted rearrangements.

(b)

741
views
Textbook Question

Under certain conditions, when (R)-2-bromobutane is heated with water, the SN1 substitution proceeds twice as fast as the SN2. Calculate the e.e. and the specific rotation expected for the product. The specific rotation of (R)-butan-2-ol is −13.5°. Assume that the SN1 gives equal amounts of the two enantiomers.

1242
views
Textbook Question

A reluctant first-order substrate can be forced to ionize by adding some silver nitrate (one of the few soluble silver salts) to the reaction. Silver ion reacts with the halogen to form a silver halide (a highly exothermic reaction), generating the cation of the alkyl group.

Give mechanisms for the following silver-promoted rearrangements.

(a)

1853
views
Textbook Question

Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.

Hint: Most rearrangements convert 2° (or incipient 1°) carbocations to 3° or resonance-stabilized carbocations.

(d)

724
views
Textbook Question

For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).

c. 1-iodo-1-methylcyclohexane + ethanol

763
views