A substituent capable of a
+R (e.g.
NO2) or
−R (e.g.
OCH3) effect, respectively.
See: σ-constant, electronic effect, polar effect
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1155 (https://doi.org/10.1351/pac199466051077)