The Many Chemists Who Could Have Proposed the Woodward‐Hoffmann Rules But Didn't: The Organic Chemists Who Discovered the Smoking Guns^[]**

Abstract

It is a reasonable question to ask, why, as of 1965 when the five Woodward‐Hoffmann communications appeared, did no other organic chemist discover the orbital symmetry rules for pericyclic reactions? Two theoretical chemists – Luitzen Oosterhoff (in 1961) and Kenichi Fukui (in 1964) had discovered portions of the orbital symmetry rules before Woodward and Hoffmann. Why not organic chemists? Indeed, perhaps the greatest motivation to discover the mechanism of a mysterious reaction is to uncover key examples of that mysterious reaction in your very own laboratory. The stories of 20 chemists and R. B. Woodward are discussed in this paper which is Paper 6 in a 27‐paper series on the history of Woodward‐Hoffmann rules. Social, political, and scientific explanations will also be presented as partial explanations as to why none of these individuals – except Woodward with Hoffmann – solved the pericyclic no‐mechanism problem.

Why Woodward and Hoffmann? And Why 1965?**

“…In Publications 2, [13] 3, [35] and 6 [112] of this series, a large number of pre-1965 experimental results were detailed, all examples of the no-mechanism reactions. Several explanations had been proposed, all based on classical 'soft' theory, none of which were satisfactory.…”

“…[58,[156][157][158][159][160] By 1965, he had published extensively on the use of theory for organic reactions. [46,161,162] There were other chemists such as Andrew Streitwieser, John D. Roberts, and Saul Winstein who had experience with the application of MO theory to organic reactions (see Publications 6 [112] and 7 [163] in this series). And these chemists had experience, or shortly would have computational chemistry experience.…”

Introduction to “The Woodward‐Hoffmann Rules. From May 5, 1964, to November 30, 1964”**

“…[35] Other chemists discussed in Publication 7 include Arthur Cope, namesake of one of the prototypical examples of nomechanism reactions; Paul D. Bartlett, one of the top physical organic chemists of the era who published extensively on the nonconcerted 2 + 2 cycloadditions; Derek Barton, the discoverer of conformational analysis; John D. Roberts and Andrew Streitwieser, both of whom wrote textbooks on MO theory for organic chemists that were published in 1961; [36,37] and Michael J. S. Dewar who discovered perturbation molecular orbital theory in 1951 [38][39][40][41][42][43] and antiaromaticity in 1965. [44] * Publications 5, [32] 6 [45] and 7 [46] discuss the many chemists who were so very close to discovering the WÀ H rules but did not do so. Publications 8 [47] and 9 (in two parts [48,49] ) discuss the two chemists who did so.…”

Revolutions in Chemistry: Assessment of Six 20th Century Candidates (The Instrumental Revolution; Hückel Molecular Orbital Theory; Hückel’s 4n + 2 Rule; the Woodward–Hoffmann Rules; Quantum Chemistry; and Retrosynthetic Analysis)

“…Whether arrow pushing and reasoning by analogy, steric effects, stereoelectronic effects, and conformational analysis, none of those heuristic models or any combination of them could (or can) explain the no-mechanism problem. An entirely new type of mechanism was needed though that was not obvious at the time to the practitioners. − And that mechanistic requirement was an application of quantum chemistry.…”