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Quantitative proton affi nities of a series of alkylamines and related ali-
cyclic and saturated heterocyclic amines were measured by equilibrium
ion cyclotron resonance techniques by Aue et al. [26] in 1976.
An
ab initio
and ion cyclotron resonance study of the protonation of
borazine was investigated by Doiron et al. [27]. The experimental proton
affi nity was determined from competitive PT equilibria with the standard
reference bases and found to be 196.4 ± 0.2 kcal/mol. But in case of
ab
initio
calculations, the proton affi nity of borazine was 203.4 kcal/mol.
Core binding energies, lone pair ionization potential and proton af-
fi nities of molecules are known to have direct correlation. The electronic
relaxations accompanying lone-pair ionization and proton attachment are
similar in character and energy.
But Lee et al. [28] determined the phosphorus core binding energies
for a wide variety of tervalent phosphorus compounds. These values are
compared with literature values of the corresponding lone pair ionization
potentials and proton affi nities. No single correlation is found between
all the core binding energies and the corresponding lone pair ionization
potentials or proton affi nities.
The absolute PA of ammonia was calculated invoking the
ab initio
mo-
lecular orbital theory by Eades et al. [29] in 1980. Calculations at the SCF
level were carried out by invoking both Gaussian-type orbitals (GTOs)
and Slater-type orbitals (STOs). The STO basis was used in CI calcula-
tions with all single and double excitations included. A correction for
quadruple excitations was considered. The zero-point energy difference
between NH
3
and NH
4
+
was calculated at the SCF level with the GTO
basis and the value obtained in the calculation for PA(NH
3
) was 205.6 ±
1 kcal/mol.
A molecular orbital study of some protonated bases were carried out by
Del Bene et al. [30] in 1982. HF and fourth-order MØller-Plesset (MP4)
calculations with the 6-31G** basis set were employed to evaluate the
proton affi nities of the protonated hydrides NH
3
, H
2
O, and HF and the
protonated closed-shell bases H
m
ABH
n
, where the two nonhydrogen at-
oms might be C, N, O, or F. Inclusion of correlation generally guided
to relatively small changes in computed protonation energies and did not
necessarily yield better agreement between computed and experimental
data. However, both HF and MP protonation energies were reasonable,
and trend in protonation energies for related bases were the same at both
levels of theory. The HF and MP relative stabilities of the isomers that
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