This idea may be expressed loosely as: the more
reactive a
reagent is, the less selective it is. Consider two substrates
and
undergoing the same type of reaction with
two reagents
and
,
being more reactive than
,
and
more
reactive than
in the given type of reaction.
The relative reactivities (in log units,
See: selectivity)
for the four possible reactions may notionally be represented as shown in the diagram.
With the positions of
(
),
(
) and
(
) fixed, there are three types of positions for
(
).
In position (i) the
selectivity of
for the two substrates, measured by
, is the same as the
selectivity of
for the two substrates, also
.
In position (ii) the
selectivity of
for the two substrates, measured by
, is less than the
selectivity of
for the two substrates,
i.e.
.
It is this situation which is in accord with the RSP. In position (iii) the
selectivity of
for the two substrates, measured by
,
is greater than the
selectivity of
for the two substrates,
i.e.
.
This situation may be described as
anti-RSP. There are many examples in which the RSP is followed, but there are also many examples corresponding to situations (i) and (iii). The RSP is in accord with intuitive feeling and certainly holds in the limiting case when reactivity is controlled by
diffusion. However, the validity of the RSP is a matter of great controversy.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1159
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
doi:10.1351/goldbook.
