The theorems at the core of density functional theory (DFT) state that the energy of a many-electron system in its ground state is fully defined by its electron density distribution. This connection is made via the exact functional for the energy, which minimizes at the exact density. For years, DFT development focused on energies, implicitly assuming that functionals producing better energies become better approximations of the exact functional. We examined the other side of the coin: the energy-minimizing electron densities for atomic species, as produced by 128 historical and modern DFT functionals. We found that these densities became closer to the exact ones, reflecting theoretical advances, until the early 2000s, when this trend was reversed by unconstrained functionals sacrificing physical rigor for the flexibility of empirical fitting.

The chameleonic properties of oxygen accounts for the diverse reactivity of O-functionalities and their profound role in organic synthesis.

Like the tale of blind men and an elephant, discussions of the anomeric effect illustrate the danger of conclusions from a limited perspective. Stereoelectronic analysis addresses this challenge and remains the most useful in predicting reactivity.