Chapter 16, Problem 16.53P

Diels–Alder reaction of a monosubstituted diene (such as ${\text{CH}}_{\text{2}}=\text{CH}–\text{CH}={\text{CHOCH}}_{\text{3}}$) with a monosubstituted dienophile (such as ${\text{CH}}_{\text{2}}=\text{CHCHO}$) gives a mixture of products, but the $1,2-$ disubstituted product of ten predominates. Draw the resonance hybrid for each reactant and use the charge distribution of the hybrids to explain why the $1,2-$ disubstituted product is the major product.