nonradical

Nonradical is an adjective used in several disciplines to indicate the absence of a radical character or structure. In chemistry, a nonradical species is a molecule or ion in which all electrons are paired, giving a closed-shell electronic configuration. Such species are typically less reactive toward radical processes and do not generate free-radical intermediates under ordinary conditions. Nonradical reaction pathways are those that proceed without free radicals, for example many ionic substitutions and concerted pericyclic reactions, in contrast to radical chain mechanisms. Common nonradical molecules include methane (CH4), ammonia (NH3), and water (H2O). By contrast, radical species such as the hydroxyl radical (OH•), chlorine radical (Cl•), or methyl radical (CH3•) contain unpaired electrons and are highly reactive.

In mathematics, nonradical generally refers to the negation of a radical notion. A radical of an ideal I in a ring R is rad(I) = {x in R | x^n ∈ I for some n > 0}. An ideal I is radical if I = rad(I); otherwise it is nonradical. For example, in the integers Z the ideal 4Z has radical rad(4Z) = 2Z, so 4Z is nonradical. The term also appears in the study of radical extensions and related structures, where a nonradical object is not obtained by adjoining radicals from a base field.

See also: radical (disambiguation), radical chemistry, radical polymerization, radical extension, radical ideal.