A COMPARISON OF CONDENSED FUKUI FUNCTION, FREE VALENCY AND UNPAIRED SPIN POPULATION AS REACTIVITY INDEXES FOR OPEN-SHELL MOLECULES

The local reactivity indices such as condensed fukui functions, free v alencies and unpaired spin populations have been calculated for a numb er of open-shell molecules at the HF level using the 6-31G or the 6-3 1G* basis sets. The chosen molecules contain only one or two unpaired electrons. In some cases both UHF and ROHF calculations have been per formed to examine the effect of spin contamination on the calculated l ocal quantities. The results obtained thereby do not differ to any not iceable extent for the condensed fukui functions. However, the other t wo indices are quite sensitive to spin contamination in some cases. Ba rring a few exceptions the three reactivity indices predict identical sites for free radical attack. The dimerisation reactions of some sele cted molecules have been considered, and the nature of the monomer-mon omer bonding in the dimers has been rationalised on the basis of calcu lated reactivity indices. Attempts have also been made to use these re activity indices to explain the preferential site of attack and the fo rmation of possible products in a few reactions involving two differen t radicals. Of the three indices considered here the free valency is f ound to be the most satisfactory.