THE EVALUATION OF PROTONATION ENERGY OF MOLECULES IN TERMS OF QUANTUM THEORETICAL DESCRIPTORS - Theoretical and Computational Research in the 21st Century - page 211

best available experimental results, was on the order of 1 kcal/mol. The
calculated PAs were in well agreement with available experimental evi-
dence. Finally, their study showed that multiple fl uorinated pyrenes follow
a simple ISA additivity rule observed earlier in benzenes, naphthalenes,
and biphenylenes [41, 42, 49-53]. The origin of this additivity was found
in the remarkable similarity of the intramolecular interference energies in
initial bases and their conjugate acids.
Howard et al. [54] in 1997 were the fi rst to calculate the PA of ar-
ylphosphines. At the MP2 [FC] level, with moderately-sized basis sets,
arylphosphine PAs were overestimated by 15 kJ mol -1 (after the applica-
tion of basis set superposition corrections).
Both experimental and theoretical PAs of limonene were studied by
Fernandez et al. [55]. Gas-phase basicity (GB) and PA of limonene were
derived from measurements of PT equilibria carried out by high-pressure
pulsed electron beam source mass spectrometry. Experimental GB and PA
were 842.5 kJ mol -1 and 875.5 kJ mol -1 , respectively. The proton affi nity of
C 10 H 16 was compared with ab initio (HF and MP2) and density-functional
predictions for the protonation energy. Theoretical calculations based on
DFT were in very good agreement with experimental results.
PAs and intrinsic basicities for nitrogen and oxygen protonation in the
gas phase of the amino acids glycine and alanine were calculated using
DFT (Dm) and ab initio methods at different levels of theory from HF to
G2 approximations by Topola et al. [56] in 1998. All methods gave good
agreement for proton affi nities for nitrogen protonation for both amino ac-
ids. However, dramatic differences were found between DFT, MP4//MP2,
and G2 results on the one hand, and MP4//HF results on the other hand to
the calculation of structural and energetic characteristics of oxygen pro-
tonation in glycine and alanine.
Using Dunning's basis set saturation approach, electronic energies for
proton affi nities for both ammonia and water were evaluated with hybrid
DFT methods by Jursic [57, 58]. It was demonstrated that the zero-point
vibrational correction for both of these PAs computed at the B3LYP/6-
311G(2d,2p) theory level was identical to the values obtained from excel-
lent agreement with values obtained by G2 and CBSQ ab initio computa-
tional studies. The fi nal PA values were 201.8 kcal/mol for ammonia and
162.4 kcal/mol for water.
A simple model to analyze charge redistribution associated with PT
reaction was derived from a classical ion transport model by Pérez et al.