Chapter 20.5, Problem 20.8P

Interpretation Introduction

Interpretation:

Among the given molecules, those that can function as dienes in Diels-Alder reaction have to be found.

Concept Introduction:

Diels-Alder reaction:

It is the reaction of conjugated dienes with double or triple bonded compounds which are known as “dienophiles”. The reaction is a $4+2$ cycloaddition reaction that results in the formation of a six membered cyclic product which is known as “adduct”.

Example:

For a diene to undergo Diels-Alder reaction, it has to satisfy the following two major conditions:

• • Conjugation:

  The two double bonds of the diene should be conjugate to each other which mean that the two double bonds should appear to have been separated by only one single bond in between them.

• • Single bond conformation in between the conjugate double bonds:

  The two conjugated double bonds should be only in $s-cis$ conformation which means the two conjugated double bonds should lie on the same sides of the single bond. If suppose the conjugated double bonds are on the opposite sides of the single bond, then it is known as $\text{s-trans}$ conformation and the dienes with $s-trans$ conformation cannot undergo the Diels-Alder reaction.

Examples for $s-cis$ and $s-trans$ conformations are shown here:

The letter “s” represents the single bond.

Cis - means same side.

Trans - means opposite side.