Chapter 9, Problem 64P

Interpretation Introduction

(a)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Alkyl tosylates undergo elimination reaction when they are allowed to react with strong nucleophilic base. The mechanism of the elimination reaction is $\text{E2}$.

Interpretation Introduction

(b)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: The reaction of alcohols with halogen acids $\left(\text{HX}\right)$ is a general method to obtain $\text{1}\text{°}\text{,}\text{2}\text{°}\text{or}\text{3}\text{°}$ alkyl halides. This method is preferred due to the formation of ${\text{H}}_{\text{2}}\text{O}$ as leaving group. The more substituted alcohols generally react rapidly with halogen acids.

Interpretation Introduction

(c)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Thiols react with ${\text{Br}}_{\text{2}}\text{or}{\text{I}}_{\text{2}}$, and yield disulfides $\left(\text{RSSR}\right)$. The disulfides compounds involve a $\text{S}-\text{S}$ bond. This reaction is an oxidation as hydrogen atoms are eliminated from $\text{SH}$ during the formation of disulfides.

Interpretation Introduction

(d)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: The ${}^{-}\text{SH}$ is a good nucleophile. Thiols are synthesized by the nucleophilic attack of ${}^{-}\text{SH}$ on alkyl halide or alkyl tosylates. The mechanism of the reaction is ${\text{S}}_{\text{N}}\text{2}$ that takes place in single step. Due to ${\text{S}}_{\text{N}}\text{2}$ mechanism the product of the reaction is obtained with inversion of configuration.

Interpretation Introduction

(e)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Alkyl bromides are obtained by the reaction of $\text{1}\text{°}\text{or}\text{2}\text{°}$ alcohols with phosphorous tribromide $\left({\text{PBr}}_{\text{3}}\right)$. The reaction yields ${\text{HOPBr}}_{\text{2}}$ as by-product. The mechanism of the reaction is ${\text{S}}_{\text{N}}2$ that results an inversion of configuration product. However, the further strong nucleophilic attack results the inversion in configuration product through ${\text{S}}_{\text{N}}\text{2}$ mechanism.

Interpretation Introduction

(f)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Alcohols are converted into alkyl tosylates by treatment with $p\text{-toluenesulfonyl}\text{chloride}\left(\text{TsCl}\right)$ in the presence of pyridine. The overall reaction converts ${}^{-}\text{OH}$ (a poor leaving group) into ${}^{-}\text{OTs}$ (a good leaving group), and stereochemistry of the reaction is retained. However, the further reaction with strong nucleophile leads to the formation of an ${\text{S}}_{\text{N}}\text{2}$ product with inversion of configuration.

Interpretation Introduction

(g)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: The opening of an epoxide/ethylene oxide ring is regioselective either it takes place with a strong nucleophile $\left({\text{:Nu}}^{-}\right)$ or an acid $\left(\text{HZ}\right)$. The mechanism of the reaction with ${\text{:Nu}}^{-}$ is ${\text{S}}_{\text{N}}\text{2}$, and the mechanism of the reaction with $\text{HZ}$ is in between ${\text{S}}_{\text{N}}\text{2}\text{and}{\text{S}}_{\text{N}}1$.

Interpretation Introduction

(h)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: The opening of an epoxide/ethylene oxide ring is regioselective either it takes place with a strong nucleophile $\left({\text{:Nu}}^{-}\right)$ or an acid $\left(\text{HZ}\right)$. The mechanism of the reaction with ${\text{:Nu}}^{-}$ is ${\text{S}}_{\text{N}}\text{2}$, and the mechanism of the reaction with $\text{HZ}$ is in between ${\text{S}}_{\text{N}}\text{2}\text{and}{\text{S}}_{\text{N}}1$.

Interpretation Introduction

(i)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Ethers are the most common organic products of nucleophilic substitution reaction. They are prepared from alkyl halides and strong nucleophiles. The reaction proceeds through ${\text{S}}_{\text{N}}\text{2}$ mechanism. The highest yields of products are obtained from methyl (unhindered) and primary alkyl halides. The synthesis of ether by this route is called Williamson ether synthesis.

Interpretation Introduction

(j)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Ethers react with strong acids, (only $\text{HBr}$ and $\text{HI}$) and yield two alkyl halides as products.

$\begin{array}{l}\text{R}-\text{O}-{\text{R}}^{\text{'}}\underset{2\text{equivalents}}{\overset{\text{HX}}{\to }}\text{R}-\text{X}+{\text{R}}^{\text{'}}-\text{X}+{\text{H}}_{\text{2}}\text{O}\\ \text{X}=\text{Br}\text{or}\text{I}\end{array}$

In this reaction, both $\text{C}-\text{O}$ bonds of ether are cleaved by two successive nucleophilic substitution reactions.

Interpretation Introduction

(k)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Sulfides are prepared from thiols by the successive treatment of sodium hydride (a good base), and an alkyl halide. The mechanism of the reaction is ${\text{S}}_{\text{N}}\text{2}$, and analogues to Williamson ether synthesis.

Interpretation Introduction

(l)

Interpretation: The product of the given reaction is to be drawn including stereochemistry if appropriate.

Concept introduction: Sulfide involves a nucleophilic sulfur atom. It reacts rapidly with unhindered alkyl halide to form corresponding sulfonium ion. The mechanism of the reaction is ${\text{S}}_{\text{N}}\text{2}$, which is concerted and occurs in single step.