A new @CT01038@ AB, each @M03986@ of which is formed by direct combination of two separate molecular entities A and B in such a way that there is change in @C01274@, but no loss, of atoms within the @M03968@ A and B. Stoichiometries other than 1:1 are also possible, e.g. a bis-adduct (2:1). An @I03130@ can be formed when A and B are groups contained within the same molecular entity. This is a general term which, whenever appropriate, should be used in preference to the less explicit term @C01203@. It is also used specifically for products of an @A00133@. For examples, see @L03510@, @M03819@, @A04388@.