Chapter 24, Problem 24.4YT

Interpretation Introduction

Interpretation:

The given conformations are to be classified as s-cis and s-trans. The one which can undergo a Diels-Alder reaction is also to be identified.

Concept introduction:

The Diels-Alder reaction is single step concerted reaction. The concerted nature of the Diels-Alder reaction means that both of the new carbon-carbon $\text{σ}$ bonds form simultaneously. Thus, both ends of the diene must be relatively close to the dienophile in the transition state. The appropriate distances are achieved only if the diene attains a geometry in which the two ends of the $\text{π}$ system are pointing in nearly the same direction, that is, s-cis conformation. The s indicates that the cis designation describes the orientation of groups about a single bond, rather than a double bond or the plane of a ring. Thus, for a Diels-Alder reaction to take place, the diene must be in the s-cis conformation.