Chapter 8.19, Problem 52P

Interpretation Introduction

Interpretation:

• The dienes that do not undergo Diels-Alder reaction has to be predicted.

Concept Introduction:

Diels-Alder reaction:

A conjugated diene reacts with a compound containing a carbon-carbon double bond.  It is a cycloaddition reaction, where two reactants form a cyclic product.

Conformation of Diene:

S-Cis Conformer: The double bonds are cis about the single bond (s stands for single), in an s-cis conformer.

S-trans Conformer: The double bonds are trans- about the single bond (s stands for single) in an s-trans conformer.

Condition for Diels-Alder reaction:

The conjugate diene must be in an s-cis conformation because when it is in an S-trans conformation, C-1 and C-4 are too far apart to react with the dienophile in a concerted reaction.

Rule: The stabilities of carbocation are,

${\text{Benzyl cation = allyl cation = 3}}^{\circ }{\text{carbocation > 2}}^{\circ }{\text{ carbocation > 1}}^{\circ }\text{ carbocation > methyl cation > vinyl cation}$