We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.
(a) (b)

Verified step by step guidance

1. Identify the reactants in each image. In the first image, the reactants are isoprene (2-methyl-1,3-butadiene) and methyl vinyl ketone. In the second image, the reactants are methoxybutadiene and acrylonitrile.
2. For each pair of reactants, consider the possibility of a Diels-Alder reaction, which involves a diene and a dienophile. The diene is the compound with two double bonds, and the dienophile is the compound with one double bond and an electron-withdrawing group.
3. Draw the resonance structures for the diene and the dienophile. For the diene, show the movement of electrons to form a charge-separated structure. For the dienophile, show the electron-withdrawing group stabilizing the negative charge.
4. For the first pair, isoprene can form a resonance structure where one of the double bonds shifts, creating a positive charge on one carbon and a negative charge on another. Methyl vinyl ketone can form a resonance structure where the carbonyl group stabilizes a negative charge.
5. For the second pair, methoxybutadiene can form a resonance structure with a positive charge on the carbon adjacent to the methoxy group and a negative charge on the terminal carbon. Acrylonitrile can form a resonance structure where the cyano group stabilizes a negative charge.

Key Concepts

Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. They help in understanding the distribution of charge and the stability of a molecule. In organic chemistry, resonance is crucial for predicting the behavior of reactants and products, especially in reactions involving conjugated systems.

Charge Separation

Charge separation refers to the distribution of positive and negative charges within a molecule. In resonance forms, charge separation can indicate the stability of a compound; structures with minimized charge separation are generally more stable. Understanding charge separation is essential for predicting the reactivity and product formation in organic reactions.

Substituent Positioning

The positioning of substituents on a molecule significantly influences its chemical properties and reactivity. In the context of the question, the 1,2- and 1,4-relationships refer to the relative positions of substituents on a benzene ring or similar structure. Recognizing these relationships is vital for predicting the outcomes of reactions and understanding the stability of the resulting products.