diradical SeeBIRADICAL.
direct effect SeeFIELD EFFECT.
disaccharide A class of sugar, a carbohydrate, cre-
ated by linking a pair of MONOSACCHARIDEs, which are
simple sugars. Examples of disaccharides are sucrose,
which is glucose joined to fructose. Other examples
include lactose, which is glucose joined with galactose,
and maltose, which is two glucoses joined together.
While disaccharides can be decomposed into monosac-
charides, monosaccharides cannot be degraded by
HYDROLYSIS. However, disaccharides can be degraded
by hydrolysis into monosaccharides.
dismutase An ENZYMEthat catalyzes a DISPROPOR-
TIONATIONreaction.
dismutation SeeDISPROPORTIONATION.
dispersed phase The solute-like substance in a colloid.
dispersing medium A substance in which another
substance is colloidally dispersed.
dispersion forces SeeLONDON FORCES.
displacement reaction A chemical reaction in which
one element displaces another from a compound.
disposition SeeDRUG DISPOSITION.disproportionation Any chemical reaction of the
type A + A →A′+ A′′, where A, A′, and A′′are differ-
ent chemical species. For example:
2 ArH+→ArH + ArH2+
The reverse of disproportionation (or dismutation) is
called COMPROPORTIONATION. A special case of dispro-
portionation (or dismutation) is “radical dispropor-
tionation,” exemplified by
.CH 2 CH 3 + .CH 2 CH 3 →CH 2 CH 2 + CH 3 CH 3Reactions of the more general type78 diradical
Experiment demonstrating the displacement of silver from solution
by copper. A copper coil is placed in a solution of silver nitrate
(colorless). After some time, the solution turns blue, and dendritic
crystals form on the coil. The copper from the coil displaces silver
ions in solution. The copper becomes ionized as copper(II), seen
as a characteristic blue color, and the silver is deposited as a
metal crystal.(Courtesy of Jerry Mason/Science Photo Library)