91Ó°ÊÓ

When two enantiomers are formed in one reaction so the product will form racemic mixture.

Because the reaction creates an asymmetric centre in the product the product will be racemic mixture.

b)

Even though both reactants are unsymmetrically substituted, they will be aligned primarily as shown because of the relatively stable tertiary benzylic cation and delocalization of the pi electros of the dienophile onto the oxygen.

Because the reaction creates an asymmetric centre in the product the product will be racemic mixture.

c) Looking at where the partial positive charges are in the two resonance hybrids of the diene shows that the resonance hybrid with the positive charge shared by a primary and a tertiary carbon is more stable. In the dienophile, a primary carbanion is more stable than a primary carbocation would be:

Therefore the major product is the 1,4-disubstituted product.

Because the reaction creates an asymmetric centre in the product the product will be racemic mixture.