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 21a,b
Chapter 11, Problem 21a,b

Give the structures of the products you would expect when each alcohol reacts with (1) HCl, ZnCl2; (2) HBr; (3) PBr3; (4) P/I2; and (5) SOCl2.
(a) butan-1-ol
(b) 2-methylbutan-2-ol

Verified step by step guidance
1
Step 1: Understand the reactivity of alcohols with the given reagents. Alcohols can undergo substitution reactions where the hydroxyl group (-OH) is replaced by a halide (Cl, Br, or I). The reactivity depends on the type of alcohol (primary, secondary, or tertiary) and the reagent used.
Step 2: For (a) butan-1-ol (a primary alcohol): (1) With HCl and ZnCl₂ (Lucas reagent), the reaction proceeds via an SN2 mechanism, forming 1-chlorobutane. (2) With HBr, the reaction also proceeds via an SN2 mechanism, forming 1-bromobutane. (3) With PBr₃, the hydroxyl group is replaced by bromine, forming 1-bromobutane. (4) With P/I₂, iodine replaces the hydroxyl group, forming 1-iodobutane. (5) With SOCl₂, the hydroxyl group is replaced by chlorine, forming 1-chlorobutane.
Step 3: For (b) 2-methylbutan-2-ol (a tertiary alcohol): (1) With HCl and ZnCl₂, the reaction proceeds via an SN1 mechanism due to the stability of the tertiary carbocation, forming 2-chloro-2-methylbutane. (2) With HBr, the reaction also proceeds via an SN1 mechanism, forming 2-bromo-2-methylbutane. (3) With PBr₃, tertiary alcohols generally do not react efficiently with PBr₃ due to steric hindrance. (4) With P/I₂, tertiary alcohols generally do not react efficiently for the same reason. (5) With SOCl₂, the reaction forms 2-chloro-2-methylbutane.
Step 4: Write the chemical equations for each reaction to visualize the transformations. For example, for butan-1-ol with HCl and ZnCl₂: \( \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} + \text{HCl} \xrightarrow{\text{ZnCl}_2} \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Cl} \). Similarly, write equations for all other reactions.
Step 5: Summarize the products for each reaction and note the differences in reactivity between primary and tertiary alcohols. Primary alcohols typically undergo SN2 reactions, while tertiary alcohols favor SN1 mechanisms due to carbocation stability. This understanding helps predict the products for each reagent.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
7m
Was this helpful?

Key Concepts

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

Alcohol Reactivity

Alcohols are organic compounds containing a hydroxyl (-OH) group. Their reactivity is influenced by the structure of the alcohol (primary, secondary, or tertiary) and the type of reagents used. Different reagents can lead to various substitution or elimination reactions, resulting in different products. Understanding the reactivity of alcohols is crucial for predicting the outcomes of their reactions with acids and halogenating agents.
Recommended video:
Guided course
01:01
How to name alcohols

Nucleophilic Substitution Mechanisms

Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile replaces a leaving group in a molecule. The two main types are SN1 and SN2 mechanisms. SN1 involves a two-step process with a carbocation intermediate, while SN2 is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs. The choice of mechanism depends on the structure of the alcohol and the nature of the nucleophile.
Recommended video:
Guided course
01:47
Nucleophiles and Electrophiles can react in Substitution Reactions.

Halogenation of Alcohols

Halogenation refers to the introduction of halogen atoms into organic compounds, often replacing the hydroxyl group in alcohols. Different reagents, such as HCl, HBr, PBr3, and SOCl2, can be used for this purpose, each yielding different halides. The choice of reagent affects the reaction pathway and the type of halide produced, which is essential for predicting the products when alcohols react with these halogenating agents.
Recommended video:
Guided course
03:45
Halogenation Mechanism
Related Practice
Textbook Question

Predict the products of the sulfuric acid-catalyzed dehydration of the following alcohols. When more than one product is expected, label the major and minor products.

(d) 1-isopropylcyclohexanol

(e) 2-methylcyclohexanol

1131
views
1
rank
Textbook Question

Some alcohols undergo rearrangement or other unwanted side reactions when they dehydrate in acid. Alcohols may be dehydrated under mildly basic conditions using phosphorus oxy-chloride (POCl3) in pyridine. The alcohol reacts with phosphorus oxychloride much like it reacts with tosyl chloride (Section 11-5), displacing a chloride ion from phosphorus to give an alkyl dichlorophosphate ester. The dichlorophosphate group is an outstanding leaving group. Pyridine reacts as a base with the dichlorophosphate ester to give an E2 elimination. Propose a mechanism for the dehydration of cyclohexanol by POCl3 in pyridine.

2034
views
Textbook Question

Write balanced equations for the three preceding reactions.

1349
views
Textbook Question

Contrast the mechanisms of the two preceding reactions, the dehydration and condensation of ethanol.

551
views
Textbook Question

Two products are observed in the following reaction.

a. Suggest a mechanism to explain how these two products are formed.

b. Your mechanism for part (a) should be different from the usual mechanism of the reaction of SOCl2 with alcohols. Explain why the reaction follows a different mechanism in this case.

1704
views
Textbook Question

Suggest how you would convert trans-4-methylcyclohexanol to

a. trans-1-chloro-4-methylcyclohexane.

b. cis-1-chloro-4-methylcyclohexane.

1405
views