Ernest Davidson's contributions of potential energy surfaces for thermal reactions of organic compounds form an important body of scientific work. His pursuit, with Borden, of the methylenecyclopropane degenerate rearrangement involving the trimethylenemethane singlet biradical with planar and orthogonal species is a classic example that also touches on the Davidson–Borden characterization of open shell, pi conjugated biradicals as either disjoint or non-disjoint systems. In a related effort with vinylmethylenecyclopropane he not only calculated all reasonable stationary points for both the singlet and triplet species, but demonstrated the preference for a conrotatory-bevel closure of a cross-conjugated 1,5 singlet biradical. Further, he pursued the classic hydrocarbon 1,3 biradicals trimethylene and vinyltrimethylene, showing in the latter case that there are no intermediates on the potential energy surface. Thus the reaction appears to proceed from saddle point to saddle point by traversing coordinates perpendicular to the reaction coordinates. He became embroiled in the Cope rearrangement energy surface that pushed the limits of approximations to the solution of the Schroedinger equation. He provided evidence that the conservation of orbital symmetry 'forbidden' suprafacial-inversion 1,5 shift of carbon in the circumambulatory degenerate rearrangement of norcaradiene is comparable in energy with the 'allowed' suprafacial-retention pathway. And he provided important insights into the captodative effects of monoradicals. Ernest understands more organic chemistry than most organic chemists. [ABSTRACT FROM AUTHOR]