Parr’s index to describe both electrophilicity and nucleophilicity

We have disclosed a new aspect of Parr’s ω value (ω = μ2/2η), which was originally proposed as an electrophilicity index, and reformed the ω value as a useful single scale from electrophilicity to nucleophilicity by introducing the corresponding ε values (ε = μη). The plot of the ω values against the ε values (ω–ε correlation) presented a fine parabola for 65 chemical species: the order of the electrophilicity is seen at negative ε values and the order of nucleophilicity is seen at positive ε values.