EXPERIMENTAL AND THEORETICAL PROTON AFFINITY OF LIMONENE

Gas-phase basicity (GB) and proton affinity (PA) of limonene were deri ved from measurements of proton transfer equilibria carried out by hig h pressure pulsed electron beam source mass spectrometry. Experimental GB and PA are 842 +/- 5 kJ mol(-1) and 875 +/- 5 kJ mol(-1), respecti vely. The proton affinity of C10H16 is compared to ab initio (HF and M P2) and density functional predictions for the protonation energy. The oretical calculations based on density functional theory are in very g ood agreement with experimental results. Our best theoretical predicti ons for the enthalpy of protonation range from 869.6 kJ mol(-1) (B3PW9 1/6-31G) to 873.9 kJ mol(-1) (BLYP/6-31G*). Theoretical calculations also suggest an important reorganisation of the molecular structure an d charge distribution of limonene after protonation.