Why Woodward and Hoffmann? And Why 1965?

Previous publications in this series on the history of the development of the Woodward-Hoffmann rules revealed why Woodward and Hoffmann were prime candidates to solve the pericyclic no-mechanism problem. This publication explains why it was the collaborative team of R. B. Woodward and Roald Hoffmann who did solve this mechanistic problem in a series of five communications in the Journal of the American Chemical Society in 1965. That is, the reasons why Woodward and Hoffmann were the perfect team, and why their individual capabilities, experiences, and qualities provided the perfect synergy are described. In part, this was the right time and the right place for them both, but the synergies were fundamental, intrinsic and idiosyncratic as a collaborative pair. Their orbital symmetry rules provided the mechanism of all concerted pericyclic reactions including electrocyclizations, cycloadditions, and sigmatropic rearrangements. Why it was 1965 and not earlier is also discussed.