Chapter 20, Problem 20.49P

Interpretation Introduction

Interpretation:

The products in the given cope rearrangements has to be predicted with stereochemistry.

Concept Introduction:

Cope-rearrangement:

It is a pericyclic reaction that involves the redistribution of six electrons through the formation of a cyclic transition state from which a $\text{1,5-diene}$ gets converted into its isomeric form.

Example with mechanism of cope-arrangement:

In this mechanism, two pi-bonds and one sigma bond of the reactant molecule has been rearranged and formed two new pi-bonds through a cyclic transition state.

Identification of cope-rearrangement in a$1,5-diene$:

In the cope-rearrangement, the flow of electrons takes place between six bonds that are bonded as $\text{C=C-C-C-C=C}$. Identification of such a bonding pattern in a $\text{1,5-diene}$ indicates the possibility of Cope rearrangement to occur as shown here:

The carbon atoms that are involving in the cope-rearrangement are shown in bold.

Stereochemistry in a product formed:

• • In the product of a chemical reaction, if a carbon atom has been attached with four different carbon atoms, then it is known as chiral carbon atom or stereocenter in the product.
• • The bonds of the functional groups because of which a new chiral carbon is supposed to form have to be represented in solid wedge bond and hashed-wedge bonds according to the particular enantiomer.
• • Racemic mixture is the mixture of two enantiomers in equal proportions.
• • Enantiomers are non-superimposable mirror images.
• • Achiral product is the product in which there won’t be any chiral centre or stereocenter.