The linear (eq 2) or quadratic equation (eq 3) could be used for extrapolation and interpolation of k0, k25, and k50. However, for long-chain compounds, the uncertainty in the extrapolated k0 value is high no matter if eq 2 or 3 is used because there are no measured k data in the low φMeOH range. The reliability of the extrapolation may be improved by using the strong linear relationship between log k and the number of CF2 or CH2 for a given class of compounds (Figure ).