Chapter 24, Problem 24.63P

Interpretation Introduction

Interpretation:

Among the given two cases which approach is favored is to be explained.

Concept introduction:

If both the diene and the dienophile of a Diels–Alder reaction are unsymmetric, then two constitutional isomers can be produced. The isomers are produced from different relative orientations of the two reactants when they approach each other. One way to understand this regiochemistry is to draw the resonance hybrids of the diene and dienophile and apply the following rule:

When the diene and the dienophile of a Diels–Alder reaction are both unsymmetric, the major isomeric product is the one produced by the approach that exhibits the more favorable electrostatic attraction among atoms undergoing bond formation. Thus, the extent of overlapping in the atomic orbitals is important.