Mn. Glukhovtsev et al., ACIDITIES, PROTON AFFINITIES, AND OTHER THERMOCHEMICAL PROPERTIES OF HYPOHALOUS ACIDS HOX (X=F-I) - A HIGH-LEVEL COMPUTATIONAL STUDY, Journal of physical chemistry, 100(9), 1996, pp. 3498-3503
The acidities, proton affinities, ionization energies, dissociation en
ergies, and heats-of formation of the hypohalous and hydrohalic acids
have been calculated at the G2 level of theory. Where reliable experim
ental data are available, our results are generally in good agreement
but in other cases our predictions serve to fill important gaps. The c
alculated gas-phase acidities of the hypohalous acids (1507.9 (HOF), 1
490.0 (HOCl), 1490.6 (HOBr), and 1487.0 (HOI) kJ mol(-1) at 298 K) agr
ee well with available experimental data and are close to one another
(lying within a range of 20.9 kJ mol(-1)), showing that the nature of
the halogen has relatively little impact on their acidity. In contrast
, the Delta H-acid values for the hydrohalic acids HX increase by 232.
9 kJ mol(-1) in going from HF to HI. Hypohalous acids are more acidic
than water. In addition, hypofluorous acid is a slightly stronger acid
than HF. However, other hypohalous acids are weaker than the hydrohal
ic acids HX (X = Cl-I). The calculated proton affinities at oxygen (HO
X --> H(2)OX(+): 565.9 (F), 641.9 (Cl), 678.0 (Br), and 724.7 (I) kJ m
ol(-1) at 298 K) and at the halogen (HOX --> HOXH(+): 488.7 (F), 581.5
(Cl), 601.0 (Br), and 642.3 (I) kJ mol(-1) at 298 K) are larger than
PA(HX) values (484.0 (F), 561.5 (Cl), 584.8 (Br), and 626.0 (I) kJ mol
(-1) at 298 K) for all the halogens. The HOXH(+) structures are higher
in energy than the O-protonated forms, H(2)OX(+). The ionization ener
gy (IE) values for HOX decrease from HOF (12.71 eV) to HOI (9.89 eV) i
n a manner parallel to that found for the IE values for HX (X = F-I).
The IE(HOX) values are all smaller than the corresponding IE(HX) value
s, but the IE difference decreases substantially in going from F to I.
The G2 heats of formation for the hypohalous acids (-88.3 (HOF), -76.
0 (HOCl), -58.3 (HOBr), and -48.9 (HOI) kJ mol(-1) at 298 K) show good
agreement with available experimental values.