MANY bitter-tasting substances produced by plants are known, but no conclusive relationship between bitterness and chemical structure has been proposed. Shallenberger and Acree1 recently related a sweet taste to certain molecular features, and reported that sweet compounds possessed a proton–donor group (DH) and a proton–acceptor group (A), and that these groups should be in positions such that the proton of the former and the orbital of the latter are at an average distance of 3 A, a distance that makes intramolecular hydrogen bonding impossible.