Zucker–Hammett hypothesis

https://doi.org/10.1351/goldbook.Z06751
This hypothesis states that, if in an acid catalysed reaction, log10k1 (first-order
rate constant
of the reaction) is linear in H0 (Hammett
acidity function
), water is not involved in the
transition state
of the
rate-controlling step
. However, if log10k1 is linear in log10[H+] then water is involved. This has been shown to be incorrect by Hammett himself.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1176 [Terms] [Paper]