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10.6 LITERATURE SURVEY ON THE METHODS OF
DETERMINATION OF PROTON AFFINITIES OF MOLECULES
The survey of literature shows that is plethora of information have ap-
peared on the determination of proton affinity both experimental and theo-
retical.
In 1964, Munson and Franklin [19] studied the energetics of some
gaseous oxygenated organic ions, and they measured the proton affi nities
of some oxygenated organic compounds. The heat of formation of some
simple oxygenated organic compounds were measured from sources;
∆H
f
(CH
2
OH
+
) = 174 kcal/mol and ∆H
f
(CH
3
O
+
) = 202 kcal/mol. The pro-
ton affi nities of formic, acetic, and propionic acids were determined from
rearrangement ions of esters as about 170-180 kcal/mol. The protonated
acid ions were readily formed by ionic reactions in the gaseous aliphatic
acids. The potential data for H
3
O
+
and CH
3
OH
2
+
were interpreted to give P
(H
2
O) ≈ P(CH
2
OH) ≈ 170 kcal/mol.
In 1966, Harrison et al. [20] used the energetic of formation of some
oxygenated ions and the proton affi nities of carbonyl compounds to esti-
mate more reliable values of gas-phase proton affi nities of a number of
carbonyl compounds.
In 1968, Beauchamp et al. [21] used the ion cyclotron single- and
multiple-resonance spectroscopy technique to identify and examine the
energies of ion-molecule reactions in which H
3
O
+
and H
3
S
+
were involved
either as product or reactant. To evaluate the proton affi nities of the H
2
S
and H
2
O, they [21] used the following scheme:
The proton affi nity (PA) of a molecule (B) is defi ned as the negative of
the enthalpy change for the reaction
B + H
+
BH
+
(2)
The hydrogen affinity (HA) could be similarly defined as the negative of
the enthalpy change for the reaction:
B
+
+ H
BH
+
(3)
From thermochemical considerations, the relations
PA(B) = ∆H
f
(B) + H
f
(H
+
) − H
f
(BH
+
),
(4)
HA(B
+
) = ∆H
f
(B
+
) + H
f
(H) − H
f
(BH
+
),
(5)
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