A comparison of condensed fukui function, free valency and unpaired spin population as reactivity indices for open-shell molecules

The local reactivity indices such as condensed fukui functions, free valencies and unpaired spin populations have been calculated for a number of open-shell molecules at the HF level using the 6-31G* or the 6-31G** basis sets. The chosen molecules contain only one or two unpaired electrons. In some cases both UHF and ROHF calculations have been performed to examine the effect of spin contamination on the calculated local quantities. The results obtained thereby do not differ to any noticeable extent for the condensed fukui functions. However, the other two indices are quite sensitive to spin contamination in some cases. Barring a few exceptions the three reactivity indices predict identical sites for free radical attack. The dimerisation reactions of some selected molecules have been considered, and the nature of the monomer-monomer bonding in the dimers has been rationalised on the basis of calculated reactivity indices. Attempts have also been made to use these reactivity indices to explain the preferential site of attack and the formation of possible products in a few reactions involving two different radicals. Of the three indices considered here the free valency is found to be the most satisfactory.