CHAPTER 9: Question 12
2D Explanations
In order for a diene to participate in a Diels-Alder reaction, they must
be able to adopt an s-cis conformation. Of the dienes shown in the
question, cyclopentadiene can only adopt an s-cis conformation and
so will be the most reactive, whilst the decalin derived diene cannot adopt
an s-cis conformation and so will be the least reactive since it
will not undergo a Diels-Alder reaction. The three remaining dienes will
exist as a mixture of s-cis and s-trans conformations, and
their reactivity
will be determined by the population of the s-cis conformation.
As shown below, the introduction of methyl groups onto the terminal positions
of the diene decreases the stability (and hence the population) of the
s-cis conformation due to steric interactions between the groups
on opposite ends of the diene system. Thus, the reactivity order is as
given below.
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