Term: selectivity factor, S f
https://doi.org/10.1351/goldbook.S05567

Definition:
A quantitative representation of selectivity in aromatic substitution reactions (usually electrophilic, for monosubstituted benzene derivatives). If the partial rate factor, f, expresses the reactivity of a specified position in the aromatic compound PhX relative to that of a single position in benzene, then the selectivity factor S f (expressing discrimination between p- and m-positions in PhX) is defined as: \[S_{f}=\log _{10}(\frac{f_{p}^{\text{X}}}{f_{m}^{\text{X}}})\]

Related Terms:
1) selectivity (http://doi.org/10.1351/goldbook.S05563).
2) aromatic (http://doi.org/10.1351/goldbook.A00441).
3) substitution reactions (http://doi.org/10.1351/goldbook.S06078).
4) electrophilic (http://doi.org/10.1351/goldbook.E02020).
5) partial rate factor (http://doi.org/10.1351/goldbook.P04421).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1162 (https://doi.org/10.1351/pac199466051077)

Citation: 'selectivity factor, S f' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.S05567

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