The experimentally determined Arrhenius equations and activation energies derived thereof are summarized in Table 4.
Clearly, when comparing the results of both independent experiments 1 and 2, reproducible data have been obtained.
The activation energy related to the formation of total iso-R-acids amounts to 96-97 kJmol-1. This result is in agreement with the activation energy of iso-R-acid formation as measured by others (98.6 kJmol-1; 9).
Furthermore, as apparent from Table 4, activation energies related to the formation of isocohumulone, isohumulone, and isoadhumulone are nearly identical.
This can be ascribed to the fact that within the transition state, the same bonds are being broken and formed during acyloin ring contraction, regardless of the nature of the R-acid being converted.
A similar enthalpy of activation will lead to a similar free energy of activation (Ea). Consequently, the influence on the activation energy of the hydrocarbon residue in the acyl side chain at C-2 of the R-acid appears to be negligible.