Skip to main content
Ch.11 - Reactions of Alcohols
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.11 - Reactions of AlcoholsProblem 49d,e
Chapter 11, Problem 49d,e

Predict the major products (including stereochemistry) when cis-3-methylcyclohexanol reacts with the following reagents.
(d) concentrated HBr
(e) TsCl/pyridine, then NaBr

Verified step by step guidance
1
Step 1: Analyze the structure of cis-3-methylcyclohexanol. The molecule consists of a cyclohexane ring with a hydroxyl (-OH) group and a methyl (-CH₃) group attached to adjacent carbons in a cis configuration. The hydroxyl group is the functional group that will react with the given reagents.
Step 2: For part (d), concentrated HBr is a strong acid and a source of bromide ions (Br⁻). The reaction proceeds via protonation of the hydroxyl group to form water, a good leaving group. This is followed by an SN1 mechanism due to the secondary carbocation formed after the departure of water. Consider the possibility of carbocation rearrangement and stereochemical outcomes.
Step 3: For part (e), the reaction with TsCl (tosyl chloride) in pyridine converts the hydroxyl group into a tosylate (-OTs), which is a much better leaving group. This step does not affect the stereochemistry of the molecule. The second step involves substitution with NaBr, where the bromide ion (Br⁻) displaces the tosylate group via an SN2 mechanism. In an SN2 reaction, inversion of configuration occurs at the carbon where substitution takes place.
Step 4: Predict the stereochemical outcomes for both reactions. In part (d), the SN1 mechanism can lead to a racemic mixture (if a chiral center is formed) due to the planar nature of the carbocation intermediate. In part (e), the SN2 mechanism results in inversion of configuration at the carbon bearing the leaving group.
Step 5: Draw the major products for both reactions, ensuring that you account for stereochemistry. For part (d), the product is 3-bromo-3-methylcyclohexane, with potential racemization. For part (e), the product is 3-bromo-3-methylcyclohexane with inversion of configuration at the carbon where substitution occurred.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
5m
Was this helpful?

Key Concepts

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

Reactivity of Alcohols

Alcohols can undergo various reactions based on their structure and the reagents used. In the presence of strong acids like HBr, alcohols can be converted into alkyl halides through protonation followed by nucleophilic substitution. Understanding the mechanism of these reactions, including the formation of carbocations and the stereochemical implications, is crucial for predicting the products.
Recommended video:
Guided course
01:01
How to name alcohols

Stereochemistry in Reactions

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In reactions involving cyclic compounds like cyclohexanol, the stereochemistry of the starting material influences the stereochemical outcome of the products. Recognizing cis and trans configurations is essential for predicting the major products and their stereochemical forms.
Recommended video:
1:38
Polymer Stereochemistry Concept 1

Substitution Reactions

Substitution reactions involve the replacement of one functional group in a molecule with another. In the case of TsCl/pyridine followed by NaBr, the reaction first converts the alcohol into a better leaving group (tosylate), facilitating a subsequent nucleophilic substitution with bromide. Understanding the mechanism of these steps helps in predicting the final products and their configurations.
Recommended video:
Guided course
01:34
Recognizing Substitution Reactions.
Related Practice
Textbook Question

Show how you would make each compound, beginning with an alcohol of your choice.

(d)

(e)

(f)

1
views
Textbook Question

Give the structures of the intermediates and products V through Z.

1
views
Textbook Question

Predict the major products (including stereochemistry) when cis-3-methylcyclohexanol reacts with the following reagents.

(a) PBr3

(b) SOCl2 

(c) Lucas reagent

1
views
Textbook Question

Show how you would make each compound, beginning with an alcohol of your choice.

(g)

(h)

1
views
Textbook Question

Compound A is an optically active alcohol. Treatment with chromic acid converts A into a ketone, B. In a separate reaction, A is treated with PBr3, converting A into compound C. Compound C is purified, and then it is allowed to react with magnesium in ether to give a Grignard reagent, D. Compound B is added to the resulting solution of the Grignard reagent. After hydrolysis of the initial product (E), this solution is found to contain 3,4-dimethylhexan-3-ol. Propose structures for compounds A, B, C, D, and E.

1
views
Textbook Question

The compound shown below has three different types of OH groups, all with different acidities. Show the structure produced after this compound is treated with different amounts of NaH followed by a methylating reagent. Add a brief explanation.

(a) 1 equivalent of NaH, followed by 1 equivalent of CH3I and heat

(b) 2 equivalents of NaH, followed by 2 equivalents of CH3I and heat

(c) 3 equivalents of NaH, followed by 3 equivalents of CH3I and heat

1
views