Chapter 28, Problem 28.11P

Interpretation Introduction

Interpretation:

The explanation for the fact that the modes, $\left[4a+2s\right]$ and $\left[4s+2a\right]$ of cycloaddition are not allowed is to be stated with the help of a frontier orbital analysis.

Concept introduction:

Diels Alder reaction is the $\left[4+2\right]$ cycloaddition reaction between a conjugated diene and a dienophile to give a cycloaddition product. It is an electrocyclic reaction in which the $4\text{π}$ and $\text{2π}$ electrons of a diene and dienophile are involved respectively. The product is formed by the $\left[1,4\right]$ addition, that is, the carbons of the dienophile are attached to the first and fourth carbon of the diene.