52nd International Chemistry Olympiad, Istanbul, TURKEY
Preparatory problems: THEORETICAL
Problem 10. Woodward–Hoffmann Rules and Pericyclic Reactions The Woodward–Hoffmann rules (or the pericyclic selection rules), developed by Robert B. Woodward and Roald Hoffmann, are used to rationalize or predict some stereochemical aspects and the activation energy of pericyclic reactions. They are for all classes of pericyclic reactions (and their reverse 'retro' processes), such as cycloadditions, sigmatropic shift, electrocyclization, ene, and cheletropic reactions. Woodward–Hoffmann rules for electrocyclic reactions System 4n 4n+2
Conditions thermal (∆) photochemical (hν) thermal photochemical
Motion conrotatory (con) disrotatory (dis) disrotatory conrotatory
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