Consider a general Diels-Alder reaction to answer the following questions. In the mechanism of any Diels-Alder reaction, how many pi electrons are moving all at once? In order for any Diels-Alder reaction to hannen the diene cannot be in the s-trans conformation. Electron donating groups on the diene and electron withdrawing groups on the dieneophile favor adduct formation. 1,4-heptadiene can undergn a niels-Alder reaction whereas 2,4-heptadiene cannot. Thinking about the stereochemistry of the Diels-Alder reaction, the reaction occurs with inversion of stereochemistry of the dienophile.