QUANTUM-CHEMICAL STUDY OF THE FUKUI FUNCTION AS A REACTIVITY INDEX .2. ELECTROPHILIC SUBSTITUTION ON MONO-SUBSTITUTED BENZENES

The Fukui function f-, and the condensed form f(C)-, are studied as reactivity indices for electrophilic substitution reactions on substituted benzenes. The systems studied are PhX with X = O-, NH2, OH, F, CN, NO2, CHO, NH3+, and CHCH2. The results were obtained from SCF and density calculations using the 3-21G basis. A comparison between the Fukui function and experimental data, the molecular electrostatic potential (MEP), the HOMO-density and the Laplacian of the electronic charge distribution was made. The comparison between the Fukui function and the MEP indicated that these two properties might be complementary to each other. The Fukui function seems to describe the soft-soft interactions, whereas the MEP describes the hard-hard interactions. The HOMO-density was found to be a poor approximation to the Fukui function f-, even when taking the (HOMO-1)-density into account. A comparison of the Laplacian of the electronic charge distribution and the Fukui function showed that the relation between these two properties is not as obvious as expected.