Chapter 6, Problem 58P

Interpretation Introduction

Interpretation:

The products of the given reactions have to be determined and if the products can exist as stereoisomers, then those have to be shown.

Concept Introduction:

Addition Reaction: It is defined as chemical reaction in which two given molecules combines and forms product. The types of addition reactions are electrophilic addition, nucleophilic addition, free radical additions and cycloadditions. Generally, compounds with carbon-hetero atom bonds favors addition reaction.

Electrophilic addition: It is a type of addition reaction in which the pi bond present in the molecule breaks as the electrophile approaches and results in the formation of product with sigma bond.

Acid Catalyzed Hydration Reaction: The reaction involves breaking of phi bonds between carbon-carbon multiple bonds and addition of alcohol to more substituted position of carbon in the molecule.

First step is the acid donates proton to the alkene which leads to the formation of more stable carbo cation.

Then, the water is added to the given alkene through acid catalyzed reaction where the water gets added to the carbo cation finally, the removal of one proton from oxonium ion (oxygen with one positive charge) using water results in the formation of product.

Halogen addition to an alkene:

The addition reaction of halides to alkenes leads to the formation of vicinal dihalide as the product. The two halogens will be on the adjacent carbons.

Mainly ${\text{Br}}_{\text{2}}\text{and}{\text{Cl}}_{\text{2}}$ undergo addition reaction with alkenes and the reaction is carried out in an inert solvent such as dichloromethane.

In general, the reaction can be shown as below.

When the bromine approaches the alkene, one bromine accepts the electrons from alkene and give them to the other bromine and a cyclic bromonium ion intermediate is formed.

The formed unstable intermediate reacts with ${\text{Br}}^{\text{-}}$ and the product is formed.

Lindlar reduction: The alkenes or alkynes can be reduced to alkanes with ${\text{H}}_{\text{2}}$ in the presence of metal catalyst $\left(\text{Pd}\right)$. This heterogeneous catalyst that consists of palladium deposited on calcium carbonate which is then poisoned with various forms of lead or Sulphur. The new $\text{C-H σ}$ bonds are formed simultaneously from $\text{H}$ atoms absorbed into the metal surface.