91Ó°ÊÓ

Question: What type of cycloaddition occurs in Reaction [1]? Draw the product of a similar process in Reaction [2]. Would you predict that these reactions occur under thermal or photochemical conditions?

Question: Draw the product of each Diels–Alder reaction and indicate the stereochemistry at all stereogenic centers

Question: (a) How many π molecular orbitals are present in deca-1,3,5,7,9-pentaene $\mathbf{(}{\mathbf{CH}}_2\mathbf{=}\mathbf{CH}\mathbf{-}\mathbf{CH}\mathbf{=}\mathbf{CH}\mathbf{-}\mathbf{CH}\mathbf{=}\mathbf{CH}\mathbf{-}\mathbf{CH}\mathbf{=}\mathbf{CH}\mathbf{-}\mathbf{CH}\mathbf{=}{\mathbf{CH}}_2\mathbf{)}$? (b) How many are bonding MOs and how many are antibonding MOs ? (c) How many nodes are present in ${\mathbf{\text{ψ}}}_{\mathbf{1}}^{\mathbf{*}}$? (d) How many nodes are present in ${\mathbf{ψ}}_{10}^{*}$?

Question: What cycloaddition products are formed in each reaction? Indicate the stereochemistry of each product.

Question:What starting materials are needed to synthesize each compound by a thermal [4 + 2] cycloaddition?

Question: Explain why heating buta-1,3-diene forms 4-vinylcyclohexene but not cycloocta-1,5-diene.

Question: How can X be prepared from a constitutional isomer by a series of $\left[2+2\right]$cycloaddition reactions? Interest in molecules that contain several cyclobutane rings fused together has been fueled by the discovery of pentacycloanammoxic acid methyl ester, a lipid isolated from the membrane of organelles in the bacterium Candidatus Brocadia anammoxidans. The role of this unusual natural product is as yet unknown.

Question: What type of sigmatropic rearrangement is illustrated in each reaction?

Question: Draw the product of the [3,3] sigmatropic rearrangement of each compound.

Question: A solution of 5-methylcyclopenta-1,3-diene rearranges at room temperature to a mixture containing 1-methyl-, 2-methyl-, and 5-methylcyclopenta-1,3-diene. (a) Show how both isomeric products are formed from the starting material by a sigmatropic rearrangement involving a C–H bond. (b) Explain why 2-methylcyclopenta-1,3-diene is not formed directly from 5-methylcyclopenta-1,3-diene by a [1,3] rearrangement.