Question:
The (2E,4Z,6Z,8E)-deca-2,4,6,8-tetraene undergoes thermal 8π electrocyclization. Two products are possible: one with a cyclooctatriene skeleton and one with a bicyclic structure. Predict the major product at 25 °C vs. 150 °C. Show orbitals.
Good feature: Distinguishes between conrotatory (thermal 8π) versus disrotatory pathways when conjugation allows alternative closures; forces use of Hückel topology diagrams.
Question:
Irradiation of a mixture of 1-methylcyclohexene and cyclopentenone gives a single [2+2] adduct. Predict the structure and explain why the reaction is regioselective despite both alkenes being unsymmetrical. advanced organic chemistry practice problems
Good feature: Requires using the excited state (n→π) of enone and FMO analysis (HOMO of alkene → LUMO of excited enone) to predict orientation from largest orbital coefficients on the enone’s β-carbon.*
Problem
Solution (one viable route)
Notes
Key concepts
Common pitfalls
Question:
Predict the product of the following thermal electrocyclization followed by a stereospecific [4+2] cycloaddition. Show stereochemistry.
Heat
(6π electrocyclization)
→ Intermediate A → + maleic anhydride (endo selective) → Product B
Good feature: Tests pericyclic selection rules (Woodward–Hoffmann), torquoselectivity, and endo rule in one connected sequence. Problem
