What products would you expect from the Diels-Alder addition of tetracyanoethylene to cis, trans \(-2,4\) -hexadiene and cis, cis \(-2,4\) -hexadiene? Explain.

Here, our dienophile is tetracyanoethylene, which has the general formula \(N=C-C=N\), and the dienes are cis,trans-2,4-hexadiene and cis,cis-2,4-hexadiene. Note: The diene should have the double bonds in conjugation (alternating single and double bonds), and the dienophile typically has an electron-deficient bond that interacts with the diene's electron-rich bond.

In the case of cis,trans-2,4-hexadiene, there's a cis conformation between C1-C2 and a trans conformation between C3-C4. For cis,cis-2,4-hexadiene, both the double bonds have a cis conformation between C1-C2 and C3-C4.

We will now perform the Diels-Alder reaction for both diene and dienophile pairs. Remember that the interaction takes place between the double bond in the dienophile and the diene's outer double bonds, leading to the formation of a six-membered ring containing a new double bond. Scenario 1: cis,trans-2,4-hexadiene and tetracyanoethylene Here, the Diels-Alder reaction occurs as follows: \[ \:\text{cis,trans}\-2,4\text{-hexadiene}\: + \: \text{tetracyanoethylene} \to \:\text{cyclohexene}\: \text{product} \] Scenario 2: cis,cis-2,4-hexadiene and tetracyanoethylene Here, the Diels-Alder reaction occurs as follows: \[ \:\text{cis,cis}\-2,4\text{-hexadiene}\: + \: \text{tetracyanoethylene} \to \:\text{cyclohexene}\: \text{product} \]

Based on the Diels-Alder reaction performed, we anticipate the following products: Scenario 1: With cis,trans-2,4-hexadiene The product formed would be a 6-membered ring with tetracyanocyclohexene, ensuring the original stereochemistry on the 6-membered ring (endo selectivity). Scenario 2: With cis,cis-2,4-hexadiene Similarly, the product formed would be a 6-membered ring with tetracyanocyclohexene, ensuring the original stereochemistry on the 6-membered ring (endo selectivity). Note: The endo-selectivity is a result of a secondary orbital interaction, which increases the stability of the transition state. In conclusion, both cis,trans-2,4-hexadiene and cis,cis-2,4-hexadiene will form tetracyanocyclohexene products with preserved stereochemistry on the 6-membered ring, and both reactions will follow endo-selectivity.