RC.HCH 3 + R′C.HCH 3 →RCHCH 2 + R′CH 2 CH 3are also loosely described as radical disproportionations.
disrotatory SeeELECTROCYCLIC REACTION.
dissimilatory Related to the conversion of food or
other nutrients into products plus energy-containing
compounds.
dissociation (1) The separation of a MOLECULAR
ENTITYinto two or more molecular entities (or any
similar separation within a polyatomic molecular
entity). Examples include unimolecular HETEROLYSIS
and HOMOLYSIS, and the separation of the con-
stituents of an ION PAIRinto free ions. (2) The separa-
tion of the constituents of any aggregate of molecular
entities.
In both senses dissociation is the reverse of ASSOCI-
ATION.
See alsoMOLECULARITY.dissociation constant SeeSTABILITY CONSTANT.dissociation energy The energy needed to separate a
pair of atoms.dissociation energy 79Apparatus used for chemical distillation. The liquid in the left-hand bulb is heated over a Bunsen burner, and a reagent is added from the
flask above it. The products of the ensuing chemical reaction can then be separated by distillation. The most volatile compound will boil
off at the lowest temperature. Its vapor passes into the condenser, a tube that is surrounded by a cooling water jacket. The hot vapor
cools and condenses on the walls of the tube and is then collected in the “receiver” flask on the right of the photo.(Courtesy of David
Taylor/Science Photo Library)