Radicals often exhibit reactivity characteristic of either nucleophilic or electrophilic species. An electrophilic radical reacts more rapidly with an electron-rich center in a molecule, and a nuc­leo­philic radical is more reac­tive toward an electron-deficient one. A number of procedures exist for determining the philicity of a radical. These range from sim­ple ones that involve assignment based on inspection of radical structure combined with a gen­eral knowledge of organic chemistry to complicated ones based on ab initio molecular orbital cal­cu­lations. All pro­ced­ures lead to the conclusion that nearly every carbohydrate radical is nuc­leo­philic. Most quantitative information about rates of reaction of carbohydrate radicals comes from extra­polation of data obtained from reaction of model radicals. Although this information is useful in understanding the philicity of carbo­hydrate radi­cals, it must be treated with caution when pyran­os-1-yl radi­cals are under consideration. Simple radicals are unable to model the stereo­elec­tronic effects that are critical to radical stability in pyranos-1-yl radi­cals and, con­se­quently, do not always provide a good measure of their reactivity.