A
pre-association mechanism in which one of the
molecular entities,
C, is already present in an
encounter pair with
A during formation of
B from
A, but does not assist the formation of
B, e.g.
The formation of
B from
A may itself be a
bimolecular reaction with some other
reagent. Since
C does not assist the formation of
A, it is described as being present as a spectator, and hence such a mechanism is sometimes
referred to as a spectator mechanism.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1165
