A Bracketing Method for Proton Affinity (PA) Measurements of Pyridine Radicals and Biradicals

摘要

Proton affinity is a fundamental property that relates to structure and reactivity. Very few experimental PA values are available for (bi)radicals. Hence, we developed a modified bracketing method to measure PA of radicals. Current Literature Methods for PA measurement: Equilibrium Method1 requires establishment of a proton transfer equilibrium between the unknown and a reference base or acid; Cooks' Kinetic Method2 requires formation of a proton bonded dimer between the unknown and a reference base or acid; Derivation From a Thermochemical Cycle Based on Appearance Energy Measurements; requires measurement of appearance energies; Bracketing Method (most versatile) requires reference bases or acids and the ability to differentiate between exo- and endothermic reactions.