Proton Affinity
The energy released when a gaseous species accepts a proton, measuring intrinsic basicity free of solvent effects.
Formula / equation
B(g) + H⁺(g) → BH⁺(g)
Unit
kJ/mol
In depth
Because it is measured in the gas phase, proton affinity reveals the true ordering of base strength without the levelling and solvation effects that distort solution measurements. Gas-phase and solution basicity orders sometimes disagree completely as a result.
Examples in the real world
Ammonia has a proton affinity of 853 kJ/mol; in the gas phase trimethylamine is more basic than ammonia, unlike in water.