The effect on a chemical or physical property (structure, rate or @E02177@) upon introduction of @S06076@ having different steric requirements. The steric effect in a reaction is ascribed to the difference in steric energy between, on the one hand, reactants and, on the other hand, a @T06468@ (or products). A steric effect on a rate process may result in a rate increase ('steric @A00051@') or a decrease ('steric retardation'). (The adjective 'steric' is not to be confused with stereochemical.) Steric effects arise from contributions ascribed to @S06037@ as the sum of (1) non-bonded repulsions, (2) bond @A00349@ and (3) bond stretches or compressions. For the purpose of @C01346@ or @L03551@ various scales of steric parameters have been proposed, notably @A00012@, Taft's \(E_{\text{s}}\) and Charton's \(\nu \) scales. In a reactant molecule RY and an appropriate reference molecule RoY, the 'primary steric effect' of R is the direct result of differences in compressions which occur because R differs from Ro in the vicinity of the reaction centre Y. A 'secondary steric effect' involves the differential moderation of electron @D01583@ by non-bonded compressions. Some authors make a distinction between 'steric' effects attributed to van der Waals repulsions alone, and '@S06037@' effects, attributed to deviations of bond angles from 'ideal' values.
Taft equation
van der Waals forces
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1168 [Terms] [Paper]