gas-phase basicity (GB)

When molecules or ions in the gas phase react and bond with H+ ions, the negative value of the free energy change of the reaction (-ΔG) is expressed as a thermochemical quantity. The protonation re-actions of molecules and ions have different values than proton affinity due to inclusion of chemical structure effects (entropy effect). This has an important role in the generation of multiply charged pro-tonated ions [M+nH]n+ in ESI.