pre-equilibrium (prior equilibrium)

https://doi.org/10.1351/goldbook.P04810
A rapidly reversible step preceding the @R05140@ in a @S05970@. For example:
P04810.png
See also:
kinetic equivalence
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1152 [Terms] [Paper]