https://doi.org/10.1351/goldbook.R05186
This idea may be expressed loosely as: the more @[email protected] a @[email protected] is, the less selective it is. Consider two substrates \(\text{S}^{1}\) and \(\text{S}^{2}\) undergoing the same type of reaction with two reagents \(\text{R}^{1}\) and \(\text{R}^{2}\), \(\text{S}^{2}\) being more reactive than \(\text{S}^{1}\), and \(\text{R}^{2}\) more
R05186.png
reactive than \(\text{R}^{1}\) in the given type of reaction. The relative reactivities (in log units) for the four possible reactions may notionally be represented as shown in the diagram.
With the positions of (\(\text{S}^{1}+\text{R}^{1}\)), (\(\text{S}^{2}+\text{R}^{1}\)) and (\(\text{S}^{1}+\text{R}^{2}\)) fixed, there are three types of positions for (\(\text{S}^{2}+\text{R}^{2}\)). In position (i) the @[email protected] of \(\text{R}^{2}\) for the two substrates, measured by \(a\), is the same as the @[email protected] of \(\text{R}^{1}\) for the two substrates, also \(a\). In position (ii) the @[email protected] of \(\text{R}^{2}\) for the two substrates, measured by \(b\), is less than the @[email protected] of \(\text{R}^{1}\) for the two substrates, i.e. \(b < a\). It is this situation which is in accord with the RSP. In position (iii) the @[email protected] of \(\text{R}^{2}\) for the two substrates, measured by \(c\), is greater than the @[email protected] of \(\text{R}^{1}\) for the two substrates, i.e. \(c > a\). This situation may be described as @[email protected] 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 @[email protected] However, the validity of the RSP is a matter of great controversy.
See:
selectivity
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1159 [Terms] [Paper]