Term: steric isotope effect
https://doi.org/10.1351/goldbook.S06001

Definition:
A secondary isotope effect attributed to the different vibrational amplitudes of isotopologues. For example, both the mean and mean-square amplitudes of vibrations associated with C–H bonds are greater than those of C–D bonds. The greater effective bulk of molecules containing the former may be manifested by a steric effect on a rate or equilibrium constant.

Related Terms:
1) secondary isotope effect (http://doi.org/10.1351/goldbook.S05523).
2) equilibrium constant (http://doi.org/10.1351/goldbook.E02177).
3) isotopologues (http://doi.org/10.1351/goldbook.I03351).
4) steric effect (http://doi.org/10.1351/goldbook.S05997).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1131 (https://doi.org/10.1351/pac199466051077)

Citation: 'steric isotope effect' 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.S06001

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